My threads keep getting merged because I'm asking questions about the same topic, so how do I add onto a thread I started? Do I just add the new question in with the answers people give me?

Well... practice on this one. After I reply and you read this, write your reply in the field below it and click post quick answer...

This comes up all the time.

Poor choice in wording, unfortunately.

"Answer this question" should be read as meaning "Reply to this thread" or even "Add additional comments" for the original poster.

The labeling of the button doesn't change with context, but the effect is the same. It adds a post in the same thread. A "thread" is all the responses under the same heading.

It doesn't make sense, usually, to answer your own question.
It's been brought up as a bug.