When you go into a rock climbing, it's important to know what to wear. Basically, you want to be comfortable.
A couple things to consider. I like to wear pants when I'm climbing, because when you're sitting in a harness, it's just a little bit more comfortable to have that fabric underneath the leg loops. And, also, for doing moves where maybe you're doing high steps. It's just kind of nice to have that extra coverage. Certain types of moves, like knee bars as well, it's nice to have some extra padding.
As far as the material, well, that choice is kind of up to you. There's lots of folks that like to climb in jeans. Folks who like to climb in athletic pants. But, really, it's up to you. Whatever's comfortable. Whatever you can move around in.
Keep in mind, it can get pretty hot while you're climbing. Jeans might not breath as well. But, if it's what you're comfortable in, then by any means, you can climb in jeans.
Sometimes a more durable fabric is a good choice as well. Really thin type wind pants might rip or tear pretty easily. So, try to avoid those.
And shorts are fine, but maybe not too short. If they get caught up underneath your leg loop they'll get hiked up really quickly. And those short-shorts are going to be really short-shorts pretty soon.
As far as the shirt is concerned, once again, anything comfortable. T-shirts, tank tops. Really, whatever suits your fancy.
So find something comfortable. Find something stylish. And go climbing.