To cast your vote, click on the chat icon at the bottom left of the profile icon and then on the "Votes" tile.
Under "Currently Running" you will find the polls that are still active.
Under "Ended" you will find polls that have already been closed.
Tap on "Set vote" to open a new window.
Here you can now tap on the answer options and optionally write a comment.
Finally, you only have to tap on "Set vote" and the vote is cast.
If you accidentally selected the wrong answer, you can change it by clicking on "Set vote" again, as long as the voting has not ended yet.
If you click on the arrow of the vote above, you will get a detailed overview of the vote.
Here you can vote with "Vote now" or see who voted for which answer option. Of course, only if the settings of the voting allow it.
Just click on one of the answer options and a list will pop up showing all members of the team who voted for this answer option.
If you want to know how to create a vote and which settings mean what, have a look here.