If you have a leaky roof, and your roof has standard asphalt shingles, you can repair it yourself. There are MANY instructions on the Internet, and an excellent Instructable How to replace a damaged shingle
by sbrown. You should view these valuable instructions, they provide information that I will not cover here.
This Instructables provides a few tips learned on a recent roof repair. They worked for me, may or may not work for you. But I'm pretty sure there will be some things here you will not see elsewhere.
I started with the venerable blue tarp on my garage roof. Where I live in Washington State, it started raining last week. May stop next July.