I feel like such a jerk, because I haven't accepted anyone's answers to my questions, and I can't figure out how! Could someone please tell me how?
In a nutshell, there's a grey checkmark on the left under the two vertical arrows and the vote count. Simply click the one of the answer you want to mark as the accepted answer:
You can try here to see if it works :)
Here is more detailed information on how to accept an answer and what the rules & suggestions regarding it are.