Reddit mentions of Introduction to Flight

I assume you mean just learning about rockets, not literally building your own. Building your own is a hundreds of thousands of dollars endeavor (at the cheapest) and requires regulatory approval from your nation's government - it's no easy task.

I've found that /r/SpaceX is a good place to learn the ins and outs of orbital rockets, though as you might expect it's pretty heavily SpaceX focused, so you'll learn a lot more about Falcon 9 and Falcon Heavy than other launch vehicles. The sub's wiki and FAQ sections give a very good overview of SpaceX and rocketry in general, and you should consider giving those a read.

Beyond that, the best thing you can do is seek out opportunities to learn. Do you have a favorite science, engineering, or mathematics professor at school? Talk to them about your interest in spaceflight and what opportunities there are to learn more. There are some great books out there about spaceflight as well, from historical narratives like "The Right Stuff" by Tom Wolfe, which talks about the history of spaceflight. John Anderson's Introduction to Flight was a textbook I used in one of my introductory aerospace classes, it's a bit pricey (though you can save money on an old edition) and obviously reads like a textbook, but give a good technical overview on both air and space systems.

After you've done all that, if you really want to get into the details of orbital mechanics and spacecraft design, you're going to need a college education. Are you in the United States or interested in studying here? I'd be happy to recommend some schools to keep an eye on if you're considering making a career out of this.

Edit: formatting