Easy - for beginners
COSTCO used to have a great whipped frosting for their cake, now they have a buttercream frosting. This recipe is an approximation of their original great frosting.
Mix well on mixer for vanilla mousse filling.
For chocolate you can use whipped cream (non dairy) plus chocolate syrup or use chocolate pudding (it™s easier).
For any other flavor you can pretty much use any instant pudding.
For fruit flavors use the same as vanilla but add the preserves of your preference like Strawberry, apricot, raspberry, etc.