1. Do I need previous experience?
If you have no problems climbing up a ladder, you will probably not find climbing that new an experience. Just think of the rock as a solid ladder with rungs at odd lengths and of sizes. Climbing basic surfaces comes naturally to most of us, rock climbing just takes this to a higher level, and potential exposure to falls are greater. This danger is usually circumvented by the use of safety ropes to prevent/arrest falls.
2. What kind of gear is used?
Basic climbing gear would include climbing shoes (a kind of slip on soft rubber show that allows greater reaction and more prcise placement of foot on rock surfaces), a waist harness that attaches you to a safety rope to prevent/arrest fall, karabiners to attach yourself to ascending descending devices, and comfortable loose clothes that allow maximum movement. Beside these there will also be ropes on which you will be attached while climbing.
3. Will I be safe?
For beginners the usual climbing process is called top-rope-belay. This means a rope is looped through a solid and often bolted anchor point at the top of the intended climb, both ends of the rope will be at the bottom of the climb. The climber will then be attached to one end of the rope via the waist/ful body harness he/she wears. The other end of the rope is passed through a device called a descender, attached to the instructors harness. The descender allows rope to be fed through at a controlled speed, and can be easily locked to stop rope from moving.
The instructor will pull in the rope as you climb, and should you lose your grip on the rock, the rope will not allow you to fall vertically, though yo may swig of the rock. Once you regain your traction and nerve, continue climbing, and once you reach the top and savor the achievement, you will be lowered down on the same rope by your instructor at the bottom of the climb. The act of controlling the rope from the bottom of a climb for the climber on the other end of the rope is called belaying. Therefore top-rope-belay the term. Its as safe as climbing gets.
4. How long does it take to learn?
Once you have understood the function and proper use of basic safety gear, you need to make this understanding a part of your climbing ritual. Safety will save you from falls if properly used. If not properly used, they have no value on climbs. You need to understand rope use and treatment, knots, setting up proper anchor and belay practices etc. Onece you have equipment use and safety ingrained, you could begin climbing almost anywhere with assistance, but to be able to call yourself a climber, you will need to be able to make proper judgements about climb difficulty, route of climb, safety etc and translate that into a climb that you lead setting your own safety devices as you climb. How long it takes you at least reach that stage would probably be describes as how long it took you to learn how to climb. And once you reach that stage, you can say you have learned how to climb, but its rather a continuous process then on.
5. How high are the climbs?
In and around Kathmandu, outdoor climbs would be about 40-60 meters, with indoor walls about 15 meters. Outside the valley, you could find climbs of several hundred meters, but most rock faces longer than that are found at higher altitudes and so enter the realm of mountaineering rather than pure rock climbing.