When you are logged in to your account via ssh, everything is done by passing text commands to the command line. Here is a list of the absolute most basic Linux / UNIX commands and their use:
ls
Lists Files and Directories
ls -al
Detailed List of Files and Directories
mkdir foo
Creates a directory called 'foo'
cd foo
Change to the directory 'foo'
cd ..
Go up a directory
cd ~
Go to your home directory
rmdir foo
Removes the directory 'foo'
rm file
Removes a file named 'file'
rm -f file
Forces the removal of a file called 'file' without prompting you for confirmation
wget url
Download a file from a web address to directory on your site