Get a copy of "Bash Guide for Beginners" at tldp.org
BUT: Here is a suggested way of learning the CLI in stages:
Open a terminal--it will start in your "home" directory
Type "ls"---this will list all the files and directories in your home folder
Type "cd", followed by the name of any directory that is showing (d at the beginning of the ls entry) Now you see the contents of that directory
Type "cd" to get back home
type "mkdir stuff" to make a new directory
pick any of the files in your home directory (ls again if you need to)
Type "cp filename stuff/"
Type "cd stuff"
Type "ls"---now you should see the file you just copied to the "stuff" folder.
You now know more about the command line than 90% of the planet....
NOW, look at the man pages for the commands you just used, eg: "man ls" This will show you all of the syntax and options available. Try some...
Next, type "info coreutils" This gives you a terse intro to some of the most basic bash commands. Again, try some....
NOW--arm yourself with beverage, pipe, slippers--other accessories--and start reading the Bash guide.
Allocate equal time to reading and doing and you will learn a lot very quickly.
