Where is the "add plugin" option?

Hi, I am installing my first plug in or at least trying to. My site is http://www.modernslice.com. My host is Host Gator. I transferred the site to Host Gator. I am not trying to figure out plugins. I have my FTP information but I do not see where the “Add plugin” button is on my dashboard. Do I need to enable this somewhere? Thanks, Laura