Hi, im new to making games and this is my first game jam. I was wondering if the sprites had to be 16x16 pixels wide and tall, or 64x64 pixels wide and tall.

As far as I understand it, the entire game has to be 64x64 pixels, not the sprites, take a look at the examples.

Indeed. Characters can be whatever size you want, game's world can be whatever size you want. The only rule is the rendered resolution (the camera if you will) is 64x64.