How to identify miniature parts that correspond to in-game enhancements?
I recommend you check out the Modelling Section of the Advanced Tau Tactica forums. This will probably be more helpful for their great magnetization guides, but there are a TON of other guides linked there... if you stick with Tau it will be an invaluable resource.

If you can find a copy of some of the older codexs they often have better pictures of what counts as what, but to some extent, even in a WYSIWYG tournament no one is going to check whether or not your squad has Grenades (or give you a hard time for not buying grenades even though they're modeled with them).