Yeah, that is kind of hard to see now, isn't it.

I had posted a response, but then decided to edit it, and I somehow ended up deleting the entire text.
I originally posted something about "verify an answer" rather than "suggest an answer", but then realized that I don't even see a "suggest an answer" button when I look at a thread. What I see is "verify an answer". That may be because only a moderator can "verify" an answer.
At any rate, I presume the function is basically the same. When you click on the "suggest an answer" button, you are in essence suggesting that the response contained in that particular post is the best response to the original question in the thread.