My A/C won't blow cold air. Where/how can I check whether it's a freon issue?

What is your question?

My A/C stopped blowing cold air this week. It did this when I first bought the car and Honda fixed it, but now it's out of warranty. I'd like to check and see whether it's a mechanical issue or if I just need more freon, but I can't find anything on the internet on how I would do that. Where is the A/C unit located in the car, and how do I know if it's out of freon?