Sorry if this is a silly question. If I am making a 3 layer cake, where do I put the cakeboard for support? Do I put it on top of the bottom layer, under the fondant or do I put it at the bottom of the second layer under the fondant? I suppose it goes under the fondant, because I never see a cakeboard on any of the pictures. If it is at the top of the bottom layer, how do you cut the cake?
I think you mean 3 tier, not 3 layer - I mean like 3 cakes stacked on top of each others.
No, you put the cardboard under the complete tier. Cut the cardboard same size as your cake. At this moment, you can barely see the edge of the cardboard. As you cover it with fondant, it will cover it completely.
I give cardboard under each tier - even the bottom one - if I work with the tier off my cake board. It is simply easier to manipulate the tier on the cardboard than the cake itself. Some people can do it different, but this works for me.
If you are not sure you can cover the cardboard, cut it touch smaller. I wouldn't bother, but it is up to you.
Everything you need to know to make, decorate and assemble tiered/stacked/layer cakes: