To preface this thread I want to warn those who are interested in going into the 75th Ranger Regiment that they are really hard to get these days but for those who want to wait until there are openings read on.
First off when you go to see a recruiter make it very clear to him right at the beginning that you want to go that route & won't enlist unless you have the contract in hand.
You will have to get an Option 40 contract. For instance - if you want to be an Infantryman in a Ranger Battalion you'll need to get an 11X/Airborne/Option 40 contract. What this gets you is Infantry OSUT, Airborne School & RASP, Ranger Assessment & Selection Program, formerly known as RIP, Ranger Indoctrination Program.
The requirements are "easy" - you need to pass the APFT with a minimum score of 80 in each event. I recommend a score of 100 because if RASP is full & the needs of the 75th aren't great you can get deselected out of the program with anything less. RASP is an 8 week course designed to take only the best & brightest Soldiers. My son thought that RIP was harder than Ranger School. If you pass the course you'll go to a Ranger Batt & get trained further by your unit. Sometime during your first year at Batt you'll be sent to Ranger School, a 60+ day kick in the groin. Your unit will conduct a pre-Ranger course to make sure you're ready to go.
If your Recruiter tells you that you can volunteer for the 75th Regt. while in AIT or Airborne School don't hold your breath. If he can't write Option 40s then that means the slots at RASP are full. Of course there are always DEPs dropping out & guys getting injured in BCT so it could happen.
Don't think that going to Ranger School while you're in the Army will get you in the 75th Regt. It probably won't. The unit that sends you to RS will get you back. The 82nd Airborne sends many of their Paratroopers to Ranger School. RS & RASP are two totally different but related things.