Need Help in Micro Econ.

I’ve got an exam on Wednesday, insha’Allah.

I’ve particularly been having trouble grasping the concept(s) of Marginal Revenue, Average Revenue, Average Cost, and the like.

Is there a good resource that nicely summarises such concepts?

Also, it’s all in relation with monopoly, oligopoly, perfect competition, monopolistic competition.

i pm'd u some help :)