"I am very interested in climbing but I don't know anybody who is climbing and so I don't really know where to start. When you wanted to try it out, did you just show up at a gym and asked someone to help you? How do I know what kind of routes are good for me? Should I do any specific exercises before starting it?"
As with most things, I think if you want to start climbing you should just go for it. It's kind of silly to think you have to be fit before going to the gym to... get fit. You have to start somewhere, and most people start at the beginning, which means you're not going to be very good! This is the same with yoga too. A lot of people say they need to be more flexible before they start going to yoga... but yoga is a great way to get flexible, so why wait?
The thing about climbing is that almost anyone can do it. At my gym they say if you can climb a ladder you can climb a rock wall. All rock gyms have climbing routes that vary in difficulty, which means there will be routes that you, the newbie, will be able to climb. It might be a bit difficult just starting out but those routes are designed to be as basic as possible and require very little strength or technique. As you gain strength and technique, you'll find that those routes will become easier and you'll start to try routes that are labeled as more difficult.
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In terms of doing workouts before starting to rock climb, I belong to the school of just doing something and not using the excuse of, "I'm not XYZ enough to start yet." That being said, being fit all around does help with climbing. I haven't been working out daily for the past few months and I can tell that not having that overall strength and cardio has kept me from climbing as hard as I know I could be. Climbing uses a lot of muscles, not just your arms. There's tons of core, back, and leg work, so working out on top of climbing will definitely help, but as I've said before, it's not necessary to start climbing. When I started climbing I hadn't worked out in years. If you start getting really into climbing and you want to be climbing at your peak, training through yoga, cardio, and other fitness regimens will definitely be something you'll want to do, but just starting out, it's certainly not a requirement for being able to climb.
I absolutely love rock climbing. It's one of my favorite ways to "work out" mostly because it doesn't feel like working out. It's fun and challenging and climbers are a wonderful group of folks to hang out with. I enjoy climbing because I can choose whether I want to have a solo day projecting routes on my own, or be social and hang out with other climbers while working on routes together.
I've written about climbing a couple times in the past here, here and here, if you want to read more about my rock climbing experience!