Start by opening a TERMINAL window. You can find TERMINAL in Applications->Utilities->Terminal.
Here are the essential commands:
pwd Print working directory (prints the filepath of the current directory you are in) ls List (lists the files in the current directory) cd xyz Change directory (navigate into directory xyz which is an available directory) cd .. Change to the parent directory cd ~ Change to the HOME directory mkdir xyz Make a new directory called xyz rmdir xyz Remove a directory called xyz (to delete all the files in a non empty directory, use rmdir -r) chmod Modify permissions cp file1 file2 Copy a file mv file1 newname Move or rename a file
That should be enough to get you started for now.
For further reading, here is a link with more basic unix commands
Here is a link for learning unix in 10 minutes
And here is a good introduction to Unix on the mac