What happens when I vote only for one party or the other?
You may cast a straight-party vote (that is, cast a vote for all the nominees of one party) by choosing the name of the party of your choice at the beginning of your ballot.
Cast a straight-party vote for one party. To override your vote for a particular candidate (i.e., to vote for someone of a different party), go to that race and vote for the candidate you favor. This will change the original straight-party vote for that one race. You have now voted mostly for the candidates in one party, but you voted for one candidate in a different party. You may do this to change your vote for as many races as you want.
If you cast a straight-party vote, there is no way to cast a "none of the above" vote for any individual race. You will need to vote for each race individually, leaving the "none of the above" race(s) blank.