I want to put a base under my print so that the first layer is full and even. Can that be done in Bambu or does that have to come from CAD software?
I’m not sure exactly what you mean but if you’re talking about adding an extra layer to increase bed adhesion you can enable rafts in the slider settings as shown below.
Go to support settings:
Then navigate to the raft section:
And increase raft layers to one or more:
You can add a primitive shape as a base. (Right click/Add part/Disc)