General Syntax:
7z a archive_name target parameters
Check your 7-Zip dir. Depending on the release you have, 7z may be replaced with 7za in the syntax.
Parameters:
Eg. This will prompt for a PW and hide file structures:
7z a archive_name target -p -mhe=on
Eg. No prompt, visible file structure:
7z a archive_name target -pPUT_PASSWORD_HERE
And so on. If you leave target blank, 7z will assume * in current directory and it will recurs directories by default.