^^^This!

You will get endless opinions on what type of bike to use. Some people prefer a road bike, MTB, personally I prefer a hybrid. But it's really a matter of personal preference. But, most people will find, after getting started, they want to add a few things. Rack, fenders, etc. If you purchase a bike without proper attachment points for these types of things, it can be frustrating down the road. Some bikes (especially racer/road) don't have many of these fittings, so just keep that in mind when looking to purchase. Also, like others have said, proper sizing is critical.

Everything else, you will figure out in time. Now get out there and ride! Have fun!