How do I split equity with cofounders when I don't understand cap tables?

You are splitting something that will matter enormously later, and you are doing it without understanding the instrument. That is a scary place to stand, and your unease is wise. Equity divided carelessly at the start causes some of the hardest fights a company ever has. A cap table is simply a list of who owns what slice of the company, and how those slices change as you raise money and hire people. That is all. It looks intimidating because the stakes are high, not because the idea is complex. You can learn the shape of it in an afternoon. Before you sign anything, do two things: read one plain-English guide to cap tables, and have one conversation with an advisor or a lawyer who has seen these deals. A few hours now protects years of your work. Do not split what you do not yet understand.