In-line skating is very simple to learn. Just buy the skates, strap 'em on, and go. It should take less than an hour before you're comfortable, and a couple of days before you're good at it.
Definitely buy knee and wrist pads to use initially. After a couple of times on the skates you probably won't need them, but you're going to fall a couple of times. I never wore pads, and I have the scars to prove it.
Plan to spend around $100 for a decent pair of skates. Any sporting goods store will have models that go as high as $400 - $500; save your money, those are definitely overkill. I prefer skates that have both buckles and laces as they fit me a little better, but YMMV. Try out several pairs, and pick the ones that fit you best. IIRC, they don't come in half-sizes, so look for a pair that's 1/2 to 1 size larger than your shoe size. I'd recommend lighter weight skates; they're more comfortable and you'll experience much less leg fatigue allowing a longer workout.
Wheels come in varying sizes and hardness. Larger wheels mean faster speed (mine are 72 mm, which I believe is pretty much standard, though IIRC they come as large as 80 mm). The hardness (is that a word?) you're looking for depends on the surface you'll be skating on. If you plan to skate primarily on hard, smooth surfaces, then harder wheels are better. If you'll be skating on rougher pavement, broken sidewalks, or pavement with a lot of seams or loose gravel, go for softer wheels. Softer wheels also have better traction, though I've never had my wheels slip on even wet surfaces. Most new skates come with all-purpose wheels, so you don't really need to worry too much about that when purchasing them.
Bearings range from ABEC-1 (not sure if any new skates even come with those anymore) to ABEC-7 (or higher). The higher the number, the "better" the bearings and the faster you can skate. Some people claim that the better bearings are a little more difficult for a newbie, but I never really noticed that much of a difference. Spacers (basically, the axle that the bearings spin around) can be plastic, aluminum or brass. In-line skating gurus claim that aluminum or brass are better (supposedly better for heat dissipation), but I've used all three and never noticed any difference.
Odds are, any new skates you're looking at will come with 72 mm wheels of medium hardness, ABEC-5 or -7 bearings, and plastic or aluminum spacers. Unless you become a hardcore in-line skating freak, that should easily be sufficient. All the parts are standard, so you can easily "upgrade" any time; if your parts aren't interchangeable with other brands, take the skates back (you got ripped off and bought some proprietary POS).
Skates need regular maintenance. Whenever you start to see noticeable wear on the wheels, they need to be rotated (move the first wheel on the right skate to the third position on the left skate, second wheel to the fourth position, the third wheel to the first position, etc.). All decent skates will come with a pair of allen wrenches for removing the wheels. If you're not going to take apart and re-grease the bearings (something I've never done), at least make sure to clean the dirt and grime off of them each time you rotate the wheels.
Skating is easy. Make sure the skates are laced or buckled tightly, but still comfortable. Stand up nearly straight, with your knees slightly bent. With one leg, push backward and to the side to starting moving; lift the skate up and bring it back in front of you, and do the same with the other leg. It shouldn't take very long to get the hang of it. Most people seem to have a hard time stopping, but I think it's pretty easy. My brake is on the right skate, so I balance on the left skate (knees bent, leaning slightly forward) and bring my right leg forward (keeping my foot straight) so that the front wheels come off the ground and the brake makes contact. I keep my leg stiff, and transfer most of my weight to the right leg, putting a lot of pressure on the brake. It takes a little practice, but once you learn how to do it, it's easy.
Good luck, and let me know if you've got any specific questions I can answer.
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