Ask HN: How does it normally go when one Founder invests the initial money?

Hey HN, thinking about starting my first company. The business co-founder is going to be putting up the initial money for server costs etc. until we get financing.

How do you normally write a contract around this? We've all agreed to split the equity evenly. Should we handle the money he puts up as a loan to the business? Is there something else we can do?

Tried googling for stuff, but had a tough time finding any resources.