Really?
If your garage has doors you would know!
If it's your carport ( no doors ) you would know. Call the police.
What should you do if you think a homeless person is staying in your garage?
set up some cameras in your garage before you do anything—you probably know what these will be used for. Watch the recordings from the nights every single time for around a week or a little bit less. If you see somebody in your garage and it ain’t you or anyone that should be there—congrats you got someone living in your garage. Just kick them out, or call someone who can take care of it for you. If you kick them out yourself, maybe you can give them food or a little something if you want to feel like a good person, but hey, they aren’t your problem or anyones. Just to make this clear—don’t do harsh things without knowing if someone is living there.
Lock your garage.
Call your local kopshop that is what they are there for!
Give him a sandwich and a soda
Wonder how I suddenly came into ownership of a garage.
Take him to homeless shelter.
Have him/her start paying rent. (Everyone implied that this homeless person was a stranger. Could be a homeless relative and that explains how he/she gets in your garage.)
Lock your garage
I think you need to discus about his problem and then you can give him some works and tell that - now you can manage your shelter.