Each command has different options (what you call "flags") which could mean different things, based on the command. To see a fairly comprehensive list of Linux commands, look here
. You could also see what those options mean by viewing the manual page for that command. For example, to what all the options for the "ls" command are, do this:
You move forward in the man page by hitting the spacebar, move backwards by hitting b, and you quit the viewer by hitting q.
Some commands use the "info" format for their manuals. For example, the ls command has a more detailed info manual than the standard "man page" format, so you could also do this:
You can navigate the info pages the same way as the man pages, though info pages have sort of a hyperlink feature that man pages don't have. You can use the pinfo viewer to use those (the arrow keys can be used to follow the hyperlinks). If you don't have pinfo installed, install it like this:
yum install pinfo
For now, I'd recommend just using the man command to see the basic information.