I have been a missionary nurse off and on since 2002. I lived in Honduras for 2.5 years, then did short term trips while I went back for my FNP then lived in Guatemala for 2 years and now am in Guanaja Honduras for the last year. Mission nursing is a calling most folks don't even make it 2 years - mostly for financial reasons. Most mission organizations do not pay, you fund raise your own support, typically signing up with a mission agency or as we do our church handles our donations. Some places will give you a place to live - most do not. Get on the internet and start searching. Once you find a couple of places that look interesting go there for at least a month, 3 would be better. You need to get past the visitor stage to really see if you fit with the organization. Each one operates differently and has different rules that you may or may not be able to live with.
If you plan to go to Central America or most of South America it is time to start taking Spanish. You will not be able to do a lot if you can not communicate in Spanish. Guatemala has a bunch of Spanish schools
that have volunteer opportunities that you could get involved with. It takes about 3 months of full time classes to begin to be functional with your Spanish. Some take longer. 1 month will make it so you can go to the store and buy stuff or say some basic stuff. If you start at home you can at least get a jump start on vocabulary - just make sure some one helps you with the pronunciation.
I would highly suggest getting at least a years experience before starting in the mission field. School gives you the basics but the practical application is more important. ER experience is the best (in my opinion). Learn what ever you can. Have a doc teach you to suture, ask why one antibiotic is used instead of another. Pick peoples brains. Tell them why you are bothering them and they will be more willing to give you tidbits of information. Ignore technology, in third world countries it is what I call "gut" medicine. You ask a lot of question, do the best exam you can then go with your gut - simple to more uncommon. I have diagnosed patients with everything from Malaria to leukemia, treated pregnancy to seizures. You really have no idea what the next patient is going to have and that think all nurses are doctors and since you are from the US you will have the answer to their problem
It is tough, you live in a different culture, fight loneliness, strange illnesses and frequently ask to give away anything you have. Preparation and flexibility is the key. All that being said I wouldn't change my job for the world it is fabulously rewarding.
If you have any specific questions send them my way.
Best of luck in school -Cheryl