Here's how the process goes:
After you take the ASVAB the recruiter sets a date for you and other applicants to go to a Military Entrance Processing Station (MEPS). Transportation, lodging, and food are covered by the AF. At MEPS you go through background, medical, drug screening, etc. You will get these results at a later date.
You return to MEPS (again, everything covered by the AF) and after you clear everything you get a list of jobs you qualify for (taken from ASVAB results), you choose a job, length of service, bonuses, etc. if there's something you don't like talk to that person right there and then. Don't let them force you to sign, take your time; you are not obligated to anything yet. You read the contract, ask questions, and if you like it then sign. If not, ask for what you want (you may or may not get it).
After you sign, you take an Oath to serve the country. You receive your shipping date (date you'll go to Basic Military Training - BMT). 6 weeks of training, X number of months at a technical school (job you chose), and then you are sent to your first duty station. Welcome to the Air Force.
For the reserves, you show up for duty 2 weeks a year except when you get activated and find yourself on a plane to the Middle East. I don't know the specifics of the Reserves since I was Active Duty. I've heard the atmosphere is laid-back and whatnot. Not sure. Feel free to call your nearest Reserve base and talk to everyone you can from Airmen, NCOs, AF civilians, to Officers.
Salary for reservists is different than AD (can't remember specifics); tuition, bonuses, training requirements, etc might be different as well (read: less). One thing to remember, this is not your typical part-time job: when the AF says you got to go somewhere, you really don't have a choice.
Jordan Joab.