You should probably figure out what exactly you want to do and for whom, then contact them and find out about their requirements. I'd be very surprised if the Red Cross, for example, let someone young (18) go into a hostile situation. You would probably be utilized in another effort. Part of that would be due to your lack of experience...they would want to 'season you' before putting you into the oven.
Most major organizations will require you to have some kind of 'skills' that would be beneficial to their cause.
IMHO:
A good 'over-all' skill to look into (assuming you're in the states), would be an EMT-B course. You'll learn BLS (basic life support) skills. You would also get your healthcare provider level CPR certification. Go to NREMT's site for a description of what's taught...some might not be usefull, but a lot would be in ways that might not be apparent now. (( BSI - Body substance isolation...think AIDS, HIV, 'other nasty things', etc. and how not to get them. ))
Nationally, there are 4 levels of EMT certification. EMT-FR (First Responder), EMT-B (Basic), EMT-I (Intermediate), EMT-P (Paramedic). Some states have minor differences, such as another level between EMT-B and EMT-I (WI) and some don't recognize certain levels (usually EMT-I, like KY). EMT-B is a good level to start at, most classes are around 6 months. NOTE: You have to be 18 by the time of graduation to get certified. Try and take a NREMT (National Registry of Emergency Medical Technicians) based course if possible.
An EMT-FR class is quick, but not very usefull anymore. The majority of participants at that level are police officers now-a-days. An EMT-P liscensure (some states are licensed based, some certification based) would be better, it teaches ALS (advanced life support) skills, but requires a lot more training and time to complete. You also have to be an EMT-B before you can be an EMT-P. EMT-I is not fully recognized and would still require an EMT-B certification...you'd be better off spending a bit more time for the EMT-P class than the EMT-I class.
EMT-B would provide a good basis...EMT-P would give you a lot of skills on top of the basics; like endotracheal intubation (oral & nasal), drug administration (Morphine, Adenosine, Epinephrine (IV), Glucose (IV), Nitroglycerin, Narcan, Amiodarone, Atropine, Sodium Bicarbonate, Lidocaine, Diazepam, Dopamine, Furosemide, Albuterol, etc. - some common ones), cardioversion, intravenous therapy, intramuscular injections, subcutaneous injections, manual defibrillation, intraosseous infusion, needle cricothyrotomy, needle thoracotomy, ECG interpretation, trancutaneous pacing, etc., etc..
National Registry (NREMT):
http://www.nremt.org
If you want to do medical based relief, then EMT-P would give you the most options. For anything else, EMT-B would be a nice thing to 'say I have' when they consider you.
