If you know their username, you can find them with a google search "GirlsAskGuys username", typing their username instead of the word itself, of course. You can also enter the URL www.girlsaskguys.com/user/ then their username, for example mine would be www.girlsaskguys.com/user/girlsaskguys Once you find them, you can't Follow them and you'll see their posts in your Following list and your My Feed.
If you don't know their exact username, you'll have to stumble upon them in a thread on the site.
Following someone is the best way to keep track of activity from your favorite users. When you follow someone, their posts will show up in your My Feed, which you can access from the home page, and you won't have to worry about the clutter from the rest of the site.
If you want to follow someone just go to their profile, or hover over their username and click on the follow icon (you can't follow anyone whose profile is set to private).