Struggling with Ricardian Model and Heckscher-Ohlin Model, Help?

Hi,

I have an international economics exam this week and have to answer questions based on the Ricardian model and the heckscher-ohlin model. I am struggling with the two of these as my professors notes are not very clear. The graphs and logic confuse me quite a lot, especially when put into context for essay-style questions.

Does anybody have any resources or advice for understanding these concepts? I'd appreciate any help you guys can give me. Thanks so much!