Voter approves of as many candidates as they wish, by selecting those candidate on the ballot. Voters can only cast one approval vote for each candidate.
NOTE: The Approval voting system is not used to approve individual candidates for positions. The Plurality voting system should be used for approving individuals.
How the Results are Calculated
A simple vote counting algorithm is used to count the votes cast on the ballots, and the winner is the candidate (or candidates, in the event of a tie) who receives the most approval votes.
For further details visit Approval Voting on Wikipedia