As with model airplanes, the first thing you want to do is go to your local hobby shop and find out where the local clubs are flying. Go to the field or slope and see some gliders fly. Ask questions. You'll find that most pilots are more than happy to tell you about their model. Find out if they have a training program for new pilots. You'll definitely want help if you can get it. If there aren't any local clubs then at least make sure you have a place to fly before you buy a glider and put in the time to build it.The next step is to get yourself a glider. For thermal flying you'll want to start out with something slow and stable. A Carl Goldberg Gentle Lady or Great Planes Spirit comes to mind. These fly slow and will therefore receive less damage in those first few "dorked" landings. My first was an Airtronics Olympic 650 which is currently out of production. It used just 2 channels, one for rudder and the other for elevator. For slope flying you'll have to go with your instructor's suggestions as I have never actually flown from a slope (although I hope to this summer!). Depending on how windy it is you may not be able to use a floater as suggested for thermal flying.
Once your glider is built, have your instructor check it out for proper balance and assembly. An improperly balanced glider won't fly well. Your instructor can take it up for it's first test flight and then it'll be your turn. I don't think you'll find it too difficult and will probably be making landings on your own in no time. If you don't have an instructor then you'll need to go out on your own. The following is how I managed to learn without an instructor.
I used to take my first glider to a high school practice football field and just throw it. A good hard toss straight and level is all it takes. It would never get over 15 feet in the air but I learned how to give just the right amount of input to keep it flying smooth and level and was able to practice landings. Later, I had an instructor put it up on a winch and I was then able to complete the flight and landing with no other help. I didn't worry about landing in a particular spot, I just kept flying it until it was on the ground. After that night I would use a small high-start to practice on my own. A launch on the high-start is simple as long as you follow the manufacturer's recommended tow-hook location. The glider should track almost straight up with little or no correction from the pilot.
Now that I've said that it can be done without an instructor, let me again state that you should still enlist the help of an experienced pilot if at all possible. Better safe than sorry.
When it comes to what radio to use I would recommend any 4 channel model on the market. They all work well and are reasonably priced as well. There are some very fancy computer radios with many special functions for glider use but they will not be needed until you build one of the fancy models with all of the functions. You'll know when it's time.
If you don't have a local hobby shop then you can check out Tower Hobbies on-line. They have everything you need to get started in the hobby and their prices are great. Please support your local hobby shop as much as possible. They will normally be able to match the big mail order house's prices when you take shipping and handling into consideration and they are a convenient source for all those "consumables" such as glue, etc. Of course you still have to mail order something once in awhile to keep the catalogs coming.