Welcome Jilliana!! So glad you found your way here to Cstyles! As far as working with a MAC...I have NO clue however I do think that Mod The Sims might have some kind of tutorial on this. We have a member here named Freedom and she is very familiar with this site, maybe she can assist you more. Try to send her a personal message (pm) and see if she can.
Just a suggestion and I'm just trying to help you out the best I can...even though it's not much I'm sad to say!
Enjoy your time here and I'm sure you will be made to feel right at home! Also...would love to see your creations!!