There is no "follow" button. How can I follow a question or user or topic?
This site is not a social network. It's a Q&A site. There is therefore limited support for the kind of thing you are asking for.
Below the up/down vote buttons on a question is a "favorite" button. You can click this, and it will add the question to your favorites list. You view that list from the "favorites" tab in your profile.
You can't "follow" a user (or answer) in the same fashion, although you could bookmark the user's profile or the answer's permalink.
You can acquire an RSS feed of user activity by hitting the URL
https://gamedev.stackexchange.com/feeds/user/<user number>. For example, the feed for your own activity would be here.
You can follow a question by using the star button on the left to favorite that question. When changes are made to that question, you'll see an update in the favorites tab of your profile.
There is no way to follow a user.
You can follow tags, which are kind of like topics, by marking them as a favorite. Or you can just click the tag you're interested in to see the latest questions for that tag.