It's easy, just click on a user-name and then a little pop-up opens, and then you click on "follow". Or you open the profile-page of a user i.e. https://steemit.com/@deepdarkweb (so in general: https://steemit.com/@"username") and there you have on the right-hand side a "Follow" button.

So far steemit has no "Follow-Feed" (like the Facebook Friends-Feed or Twitter-Timeline), but as far as I know are the devs working on it. So this feature should be available soon.