to display the man page for man, you will get a description of how to use the man command. Have a quick read of it, just to familiarise yourself with a typical man page. You can navigate up and down using either the cursor keys or J for down and K for up (this is because the Vim text editor uses these keys to move up and down), or Page Up/Page Down. Once you're done, press Q to exit and return to the command line.
By now, you should be able to use a few basic commands such as nano, apt-get, apt-cache and dpkg, so try looking at the man pages for these. You'll probably find that many of these commands can be used for a LOT more than you've used them for so far.
The syntax is always the same - man, then the command. For instance:
to look at the man page for apt-get.
Any time you don't know what a command does, try looking at its man page and that will give you some idea. Don't worry if it looks intimidating - it is at first, but with time you'll get used to them. Remember, they're not something you have to commit to memory, but a reference. They're there if you need help with something, but many of the things in them you may only use once in a blue moon (if at all).