My aunt is giving me her Volkswagen Rabbit for my 16th birthday. She is into cars and has been for over 15 years. She has modded it and stuff like that. She told me I have to keep it into a sports condition, so she told me to start getting into cars, how they work, and how to work on them. I also want to do the same with motorcycles. Where can I begin to learn all of this stuff.
Go on youtube and do a search using the year make and model of the vehicle and look up doing things like tune ups, brake jobs, antifreeze flushes, etc. There are hundreds of videos that teach you about cars and motorcycle maintenance and repairs.
There is lots of information about how vehicles work available online and in print. You can start reading up on that if you wish and/or take auto class at your high school.
The recommendation of taking a lawnmower engine apart is a good idea as well. A lawnmower engine is very basic compared to a car engine but the fundamentals of the 4-stroke reciprocating engine is common to both.