Each player must vote for one of the available options. They can't abstain.

The phrase "the vote is tied" refers only to when there is more than one choice that received the most votes. For example, if a 5-player vote from among three different choices ends 3 votes to 1 vote to 1 vote, the vote isn't tied.

In the case of non-secret voting, votes are cast in turn order, and each player will know the votes of players who voted beforehand.

No player votes until the spell or ability resolves. Any responses to that spell or ability must be made without knowing the outcome of the vote.

Abilities that trigger "whenever players finish voting" trigger once all players have voted or once all secret votes are revealed, but they won't go on the stack until the current spell or ability finishes resolving.