You’ll commission as a second lieutenant, once you’ve spent 24 months on active duty, you’ll be promoted to first lieutenant. You’re time in the IRR while waiting to come on active duty won’t count towards this time. The promotion clock only starts ticking once you come on active duty. Once again, you’ll spend another 24 months on active duty and then get promoted to Captain. After that, you’ll spend around 8 years as a Captain before promoting to Major if I’m not mistaken. The current stance of the Air Force is that Major will be a “give me” rank for the most part (i.e. if you haven’t screwed up and you’re a decent officer, you’ll be promoted). However this may change in the future as the needs of the service change. During the RIF’s a couple years ago, Captains who weren’t exceptional were being asked to leave the service rather than be promoted.
Officer promotions are unique in that they are based on time in grade and not skill sets or job knowledge. Granted, you’ll still have to eventually get a masters degree the higher up you go, but there will never be a test that you have to take to promote (unlike the enlisted rank structure.)