Types of Climbing:

Indoor Climbing:

With indoor gyms popping up in every major city, getting a day pass at one of these facilities is definitely the easiest way to try climbing for the first time. An indoor climbing gym has artificial holds (that mimic features found on rocks) set on the wall.

The routes usually are colour-coded and are set in a way that forces a particular movement. So if you use, say red coloured holds up a wall, it will be of a particular difficulty. The starting hold(s) and the end hold are defined and a climb is considered complete when you get both hands on the end hold.
A climbing gym usually will have a handful of such routes in different grades (difficulty levels) and these routes are reset once every few months! Indoor walls usually have bouldering, top rope climbing, lead climbing and speed climbing.

Indoor Bouldering:

Bouldering walls are usually 10-15 feet high. They have cushioned mats spread all through the floor making the falls safe. Bouldering appeals to most people because of its simplicity. You don't need ropes or any other gear; a pair of rock climbing shoes and some chalk are all you need to get started.

Having a partner to boulder indoors is not a necessity, although it can help with the motivation. The routes here are called ‘problems’ and the grading system used to measure difficulty are the Font scale (e.g. 6B) and the V scale (e.g. V3) (charts in the grades section).

Indoor Top Rope Climbing:

Top rope climbing is usually the popular style of roped climbing indoors. The rope is pre-fixed on the top anchors and the two ends come down to the climber and the belayer (the partner who takes in rope to ensure the climbers safety).
Some gyms have auto belays, a device that automatically retracts rope as the climber progresses up the wall, and lowers the climber back down smoothly once he falls. The routes here too are usually colour-coded and gyms have multiple routes of varying difficulties. The harness, belay device and the carabiners are usually available in the gym.

Most gyms have trainers who can belay you as you climb up and after a few weeks you can choose to learn to belay. Gyms let you belay only after you pass their belay test and get a belay certificate. The popular grading system followed here to rate difficulties are Yosemite Decimal System (e.g. 5.10d) and the French scale (e.g. 6a) (charts in the grades section below).

Indoor Lead/Sport Climbing:

Lead/Sport climbing is when the climber takes the rope from the ground (no fixed rope at the top) and clips the rope into pre-drilled bolts in the wall. So if the climber falls, he’ll fall more than twice the distance that he has climbed up above the last bolt that he clipped. In short, the falls are a bit more serious and belaying is more nuanced than top rope climbing.

Indoor sport climbing is usually really safe given you learn the skills and take all the safety measures. Gyms usually have lead courses and certifications that you can apply for. The popular grading system followed here to rate difficulties are the same as top ropes, Yosemite Decimal System (e.g. 5.10d) and the French scale (e.g. 6a) - charts in the grades section below.

Outdoor Climbing:

Most of the skills learnt in the indoor gym translate well to the outdoors but there are also some major transitions between the two. The major difference between the two being that the holds here are not really defined. Just after a few weeks indoors, you can start venturing outdoors and start climbing with experienced climbers.

Bouldering:

The two main differences between bouldering indoors and outdoors are that the holds aren’t defined and falling consequences are much higher. Most boulder problems, you can use any feature on the rock except in rare cases where the guidebook specifically mentions eliminating a hold or two to make a variant more challenging.

You have to carry foldable crash pads that you open up under boulders to serve as your landing area. Since these pads aren’t big enough to cover all potential fall areas, a partner who spots you is also highly recommended.

Outdoor Top Rope Climbing: