First of all read this FAQ so you'll know what to ask when you rent equipment, then go take a lesson from a certified instructor.
A good point to keep in mind here is that it doesn't have to be painful. Taken slow and with the right guidance boarding can be quicker to learn than skiing. Most resorts will have qualified snowboard instructors on staff. Most boarders who have also skied agree that boarding is initially more difficult than skiing but after learning the basics the intermediate and advanced levels are achieved more quickly. Edging and balancing skills are more important from the outset because your feet are secured, you can't step from foot to foot, and you don't have the use of poles as skiers do.
Snowboarders fall differently than skiers do. Where skiers tend to fall to the right or left snowboarders fall forward or backwards onto their face or butt. It is best in a forward fall to fall to the knee and forearm (do not stiff arm on the palms) and then lift the board in the air until you stop. In a backwards fall it is best to go to the butt and roll onto the back, keeping the chin in your chest. Learn to ride with fingers in a fist, to avoid finger smashing. And why not have releasable bindings? Most boarders would disagree with the use of a releasable binding, the board is relatively short, most ride a 140-165 cm length board, and the idea of going down a hill with one foot released and one not is a very scary thought.
Most ski areas require snowboards to have leashes. Boards today are lighter, easy to turn and comfortable to ride. Make sure the boots you rent or borrow fit as well as possible. The right boots give your ankles much needed support and alleviate pressure points from the straps or buckles. Hard boots and plate bindings are not recommended because of the increased difficulties of balancing, turning, skating and using lifts.
A beginner should learn on an freeride board that's slightly more flexible or shorter than their friends of the same weight might have.
There now are a few books out there on snowboarding which include how to sections written by professionals. A newer one, I found very good, is entitled The Complete Snowboarder by Jeff Bennett and Scott Downey. Read about it if you want to, but then go get a lesson!