Where do you guys get this stuff?

I'm serious. I get all kind of information here that I don't see in any of the books I look at in the stores, or in the MS knowledge base, or on any internet sites.
For example, I have seen (and asked about) ways to filter a list. But when I go the resources I have found, I don't see anything like it in the examples, etc. Like =countif($e$1:e1,e1). I'm fairly new to this stuff. I know this works for what I want to do. I might work backwards and see the logic as to how it works. But I've seen nothing anywhere which would lead me into knowing this would count the instances and give an incremental number that could be used to filter. I don't mind reading on my own and learning and not bugging people with what may be elementary questions. Is there a book or books you can recommend that will be better than what I have seen at Border's, etc?? Anything other than the counting apples example I see at all the MS sites.