FTP and hostgator setup

I’ve abandoned continuing building my site over the last two days because of a couple roadblocks. I don’t fully understand what FTP or SFTP is, why I need it and how to set it up.

I downloaded WordPress.org to my computer and installed it. My site (www.joeinsider.com) is up and running. I tried to set up cyberduck through hostgator, following the instructions closely, and fail each time. I also don’t understand why hostgator has like four ftp accounts for me. I don’t know which to use or how to set it up.

Thanks in advance.