I am getting a new car and I am planning on making a lot of modifications to it, but it is gonna be expensive if I have to pay someone to do it. How do I learn how to make car mods on my own, like changing out a stock radio for a after market one, changing rims...etc
Buy a Basic Tool Set, And a Mitchel's manual for your car.
If you are not planning on going Pro - Craftsman Pro Line is a good balance between cost and performance - don't let the name fool you, they are simply good homeowner grade tools... When you depend on your tools for a living it is either Snap-On or Mac Tools and a $20-30K investment in tools but you will not need that level for home wrenching.
Find a Mentor.
Take an Automotive Service Class at your local Tech or Community College ( probably the best and most time efficient choice )
Tires and Rims Pretty much require Shop tools for mounting and balancing - not a practical home project :)
Search the questions you have on the internet, then you can find the answers you want. Also you can purchase some car repairing books and learn it by yourself, or consult the people who is good at repairing, then one day you can do it by yourself. Practice makes more perfect.