United Airlines and its sister company Copa Airlines is your best bet for flights across Latin America. There are other local airlines you can use to hop around from your initial destination, but starting with United is usually easiest.
Make sure to sign up for a United Mileage plus number. You will get miles that can be redeemed for other travel expenses later on. Make sure to visit the other offers page, as you can rack up miles from dining, hotels, car rentals, and others.
If you were to consolidate all your travel into getting miles back, you will eventually earn a free trip.
I use United and Copa Air exclusively, as well as a United Credit Card. I have earned multiple round trips to Central America from Houston, Texas over the years by doing so.
The best online and free program out there right now is DuoLingo. You can get Spanish and Portuguese lessons and tests for free.