In this Q&A forum you'll see voting buttons to the left of each question and each answer, like this:
If you, too, would like an answer to a posted question, click or tap the up-arrow to add your vote.
If you like a particular answer, you can click the voting button beside it to indicate that.
Note, that the voting tally on the main forum screen displays only the votes for a question, not for an answer.
So if 3 people have voted up the question and 9 people have voted up the answer, the main screen tally will show 3 votes.
It's also possible to vote a question or answer down if you so desire.