Multi-Vote questions are those where the participant/voter can select more than one answer.
This is useful in elections, or just in cases where the question is: "Pick your 3 favorite animals"
Once you upload the presentation to CloudVOTE, it should ask you to do a slide review. If you cancel it, you can always click on the View Slides button to go to slide review at any point.
In slide review, click the "Is this a question?" box, then check the "Is this a multi-vote slide?" checkmark to allow multiple answers to be received from each participant.
In this mode, you have a variety of other options - set how many answers do you want to allow from each voter, whether or not to allow repeat votes (for the same answer) and whether they can select up to (flexible) X answers, or they must vote X times (fixed).
Do test this as a participant yourself...so that you can see what the voting buttons look like and how they behave in this mode.