Generally you will use the comp viewer 80% of the time. Layer viewers are used, when a layer-centric tool (Paint,Tracking,Puppet) invokes them, which these days usually happens automatically. Furthermore you can use them, if you want to compare the result of a layer without effects vs. the processed one by turning of effects rendering in the layer viewer. That's useful for color correction for instance. Likewise, since each viewer can have its own zoom level, you can work on fine details e.g. when masking, while keeping an eye on the comp viewer to see "the big picture". A last thing is to more precisely control in- and out-points similar to an editing suite. That last use is also one of the rare cases where you will use dedicated footage viewers for anything else but really just reviewing the source footage.
There are some links on these pages that should point you in the right direction:
I do have to ask, though. You say that you looked all over the place. Did you start with the first two pages of the "User interface" section of the After Effects Help document and just miss these resources, or were you looking somewhere else? It's my job to make sure that people can find what they're looking for, so I'd really like to know what you're trying so that I can improve the experience.
Sorry for the post Todd, guess I'm just in over my head. As for 'looking all over the place' I always start with F1. I tried 'comp viewer, layer viewer, and footage viewer.' Next I go to YouTube to look there for any basic tuts, I also try Google, Adobe TV, lynda.com, and sometimes creative cow, and aetuts. I read over what I can understand, but at the end of the day, a simple real world explanation like Myleniums does me a world of good (Thank you Mylenium). I knew I was going to be in trouble the minute I posted that. As I mentioned earlier, I'm a senior member on the Sony VMS board and over the years I have answered every question I knew the answer to, all the way down to 'How do I open the program?' Having said that, I'm not sure I would have even bothered answering my own question I posted here..................:/ This board seems to be geared more towards the 'power users' (which I'm clearly not). Sorry again, and thanks for the links.
There's certainly no need to apologize. We are here to answer questions.
It's also my job to try to pre-emptively answer questions by putting information in various documents (like the After Effects Help document) and making sure that they're easy to find. If you didn't find the information that you're looking for, I want to know why. So, thanks for answering and giving me an idea of what search terms and strategies you were using.
A tip: When looking for basic information, don't do highly specific searches. Instead, read through the first few sections of a chapter of After Effects Help to 1) learn the terminology for further searches and 2) find links to general introductory resources.
Regarding the second point: Googling all over the place or searching YouTube is going to just be frustrating. There's a lot of crap out there. There are a few people (including me) whose job it is to find the good materials and link to them and put them in our custom search engine. If you trust us to do that and start by reading the introductory sections of Help, I think that you'll find that we point to some good stuff on these other websites that you mention---without bringing in the garbage.