I am doing my first tiered cake. It is an 8" round and a 6" round. Do I have to use dowels and cake boards in between the tiers or can I just stack it on top?
You definitely have to use dowels and a cake board.
yes yes yes! Dowel and cake board. Otherwise you might be sorry! I also do a center dowel.
I have never just stacked them. I always use dowels and cake boards. I think the weight of the top tier would be too much. It just seems too risky. It's not that much trouble for the peace of mind.
ditto ditto!! if you don't, the top cake will just shift and sink into the bottom one.
You will only need 3 or 4 drink straws to support a 6" cake. Put it on a cake board (covered) the same size as the cake.
It is good practice for later General rule of thumb is to dowel/support every 4" you go up.
Probably won't need to use a center dowel thru the 2 tiers - especially if the cake is not being transported.