"When do I add the sugar and vanilla to my whipped cream‚ at the beginning, or after it is whipped?"
Whip the cream alone to soft peaks: the point at which when you raise your beater, the peaks flop over. That's when you should add the sugar and the vanilla. If you add ingredients too early, the cream won't whip enough and if you add them too late, you will over-whip in order to add them in.
For more tips, watch our video How to Make Whipped Cream.
Recipe: Classic Cream Puffs