Probably the most commonly used web site for searching the index of OPRs is FAMILYSEARCH.org provided by The Church of Jesus Christ of Latter-day Saints.
The are two search types used on this site :
Advanced reached by clicking the Advanced Search link on the standard page
As the Advanced gives you everything that Standard does and a LOT more I only use Advanced so that's what I'll tell you about.
Dark Area on the Left of the Screen
Although it doesn't look like it, this darker (green?) box is actually a menu, by clicking on an item you can narrow the your search down to a particular database, in general it is set to All Resources, if you click on an option the screen will change to a specific one for that option and it will contain a description of the database that the particular page searches. The screens will change slightly depending on the database selected.
Now we'll try some searches with real data, I'll use my family as an example as I know they are in there. My Great, Great, Great Grandfather George Scott was born in Roxburghshire sometime around 1826 to George and Helen Scott, but looking for a Scott on the Borders region of Scotland is not easy as that's their traditional home.
So we fill in the boxes like this using All Resources.
Note : that I set the year range to + or - 2 years and I didn't Use exact spelling. Don't narrow your search too much or you won't find your ancestor, unless you are absolutely sure the the event you are searching for happened in a particular year, always set a year range. I start with +/- 2, if that doesn't work then increase it. In my experience NEVER check the Use exact spelling box, too many errors occur with names, the writer didn't know how to spell, the writer's scribing is awful, the entry is illegible or damaged, the transcriber got it wrong or the person being described changed the spelling etc, etc.
OK we hit the button and get 48 hits, too many. However have a look at the results, we can see that the results are from several different categories, Ancestral File, Census - 1880 US Census, Census - 1881 British Census, Census - 1881 Canadian Census, International Genealogical Index - British Isles and Pedigree Resource File! We are only looking for a Birth/Christening so we don't need the other stuff. So we would be better to narrow down the search a bit.
Since we want to have solid proof of what we find, we will need to look at the Microfilm Reels containing the OPRs eventually so for a start let's search only the OPRs or as they are known in this search engine the International Genealogical Index. So hit the Back button and return to the Search Page now click on the International Genealogical Index. The page will change and we can enter the same data as above, but we now have extra criteria so we fill it in as best we can, ignore the last three boxes, and we get
Hit the Search button and we get 11 hits, much better. Now we can do two things, either click on each of the entries to look at them to see if any is the correct one and as it happens the first one I get is correct, OR we can return to the search screen and add the other information we have, father - George Scott, mother - Helen press Search again and Bingo only one hit - the correct one.
However I can say the entry is correct because I know GGG Grandmother was Helen Beattie, but what if you still have more that one entry, what do you do? It depends what other information you have, if you have no other information then just note down the details and mark it as possible. If you find corroborating info later you can always firm it up.
If you know that George has siblings then can you find siblings of the same parents?
Go back to the Search screen, remove George Scott from First & Last Name, clear the Year and Year range boxes and you should have
Hit the Search button, OOps 34 hits - some family!, however look closer, the births cover a date range of 1771 to 1853, Somehow I don't think Helen bore kids over an 82 year period!!
Go back to the search screen and add Helen's surname Beattie, Bingo - the whole family.
Now you would go through the entries one by one and check the entries for anomalies and when happy note the details down.
I beleive that if you are going to use an LDS Family History Center then you may need the Source Information but normally you don't.
So what do we have, 15 items but only 5 or 6 different names, what's going on? If you look at the entry for Helen Scott you will find only a christening date. I consider this to be the most usual result in which case it is normal practice to use the Christening/Baptism date as a birth date, however be careful, the reason that items were recorded in the parish records wasn't because they knew that in a couple of hundred years people would come looking for information, it was because christenings, banns, marriages and burials all cost the family money and therefore we are actually looking at the parish accounts.
This means that quite often the early children of a marriage will not be baptised immediately - the family couldn't afford it! It also means that you will quite often find that when a second or third child is born, the earlier ones get baptised at the same time, it can be confusing.
Anyway if you look at the first, second and third entries, which are all for Cecil, you will find that they are identical and unusual, they give birth, christening and death, therefore you get a hit for all three.
Unfortunately a fairly common story for the time, of the seven children only two survived into maturity, George and Helen who died at 64 and 89 respectively.
Warning : If I've said it once I've said it a thousand times, when it comes to Family History Research I seem to have the most phenomenal luck, you may not have the same success.
Anyway we now have George's birth along with his siblings, what about George and Helen's marriage?
Back to the Search Screen Remove Father & Mother and clear the County and put
Hit Search and we have the marriage, 3 hits all the same couple, the third entry is a Form submitted by a member of the LDS Church, be very wary of these entries they aren't checked so may be inaccurate, in fact in this case the date is wrong and the spelling of Helen's surname is wrong. The other two are different dates and places, don't be put off it was common in those days to be married in the husband's parish and the wife's parish or have the banns read in both parishes. You may also find an entry in a home parish, recording that a person or couple were married elsewhere. In addition the IGI says that it's a marriage taking place, this isn't necessarily true it may only be that the reading of the banns are recorded.
The reason I suggest you set the county to All Counties is that marriages often took place outside the couples own parishes, so in this case don't narrow the search too much.
All data found using the IGI should be checked by looking up the OPRs if possible and reading the actual entry, you never know what you will find. Indices only contain the information they need to be an index, there can be all sorts of interesting information in the actual record.
in addition the OPRs may, and often do, contain entries that for one reason or another do not appear in the indices.
So now I have the dates of a marriage and the births and in some case deaths of the children, DON'T be content with this, look up the actual records, you never know what you will find.
B.T.W. One of the reasons that George Scott's family is so well documented is that he was the Local Schoolmaster and Session Clerk, so naturally he would make sure his family's details were correct if it was he who wrote the book!