Stephanie covered much of this more succinctly than I...
Race school is on Friday. It's a long day, with a "mock start" for the last on track session of the day. After that you go through registration to sign up for races the next day and get your LRRS account (you don't have a license yet).
Saturday, first race of the day is the rookie race. The goal of the rookie race is to finish. If you can finish the rookie race with out crashing or breaking too many rules, you will then "be licensed" (you won't get your license until it comes in the mail later, but you are licensed). On a middle weight (R6) you'll be eligible for 4 (not counting the rookie) races. The schedule is different each weekend, so there is no "defined" time between the rookie race and your first "real" race, but they are pretty good about not making them back to back.
Updated previous information with some closer costs... Still pretty close. This of course assumes no tip overs, and you show up with a prepped bike and good consumables (pads, tires, etc.).
The first weekend everythings going to be going very fast. You'll be dressing and trying to head out to the pre-grid way too early. Every time. This is where having some friends really (really, really) helps. People pay attention to what races others are in and help with stands / warmers all kinds of stuff.
Garage space. There's been a tradition of a rookie garage. There's also been rumors of it not being available to rookies because there are "squatters" using it. My advice is to have a garage plan before showing up for the weekend.
Here's what my first weekend was like...