How do I get my character to collide with an object, he dies, and respawnee at the beginning of the map?

Your question does not match the unity answers guidelines, you are not specific enough.

If you want us to help you on your code, try to do something and post it here at least. If you want general guidelines, you shouldn't rely on this forum but use your capacities, you will learn a lot with trial and error.

But here is a starting point : you can use "onTriggerEnter" or "onCollisionEnter" and change the character position from here.