Here is a pretty good guide with a lot of examples that will be helpful:

https://startupguide.hbs.edu/people/founding-team/key-terms-to-include-in-a-founders-agreement/

Everything I read in the guide agrees with my own experience from my past two startups.

After reading through that guide, you can look at this more detailed customizable outline of a cofounders agreement, which has various options embedded in it for key decisions.

https://www.law.upenn.edu/clinic/entrepreneurship/startupkit/founders-agreement.pdf

The options in it are ones that you will have a general understanding of from the previous guide.