comprookie2000 has mentioned using the "man page", you'll probably have installed them with the OS (normally default!). But to view them you'd have to open a terminal (or konsole or whatever you may call it). Then if there is a man page available for "apt-get", there's a link in my sig to explain (pretty much in idiot terms - no criticism intended, I prefer my instructions in idiot/"monkey see, monkey do" terms) how to decypher the man page!
apt is a very clever bit of software, but to be able to do more than just install stuff you'd have to read up on it.
Install is either
(where xxxxx is whatever you are trying to install) or
apt-get install xxxxx
Sorry I don't recall which. The packages you'd be installing with apt, would be .deb anyway - and they're available for lot's of stuff (there's in excess of 10000 of them!).