What is conftest.py for in Pytest?

I'm trying to understand what conftest.py files are meant to be used for.

In my (currently small) test suite I have one conftest.py file at the project root. I use it to define the fixtures that I inject into my tests.

I have two questions:

1. Is this the correct use of conftest.py? Does it have other uses?
2. Can I have more than one conftest.py file? When would I want to do that? Examples will be appreciated.

More generally, how would you define the purpose and correct use of conftest.py file(s) in a pytest test suite?