ls is the command to view the files in a directory.
pwd tells you which directory you're currently in.
cd changes directory.

Suppose you were in a directory called /foo. You typed ls and found out that there were three directories in /foo - hat, ball, and cup. You want to go to cup. So you type cd cup.

To move up to the directory above the one you're in, you type cd .. So, if you were in /ball, cd .. would take you to /foo.

cd / will take you to the root of your filesystem, the directory all the other directories are in.