How to mix my own paint?

I got a hvlp sprayer for Christmas and I've studied up on the ratios, thinner, viscosity and general best practices for the sprayer itself. Setup, cleaning, technique, filters and all that. Lets pretend I have that figured out and jump to how can I mix my own colors?

I've mixed press ink in the past and that was a matter of a scale and 40g of cyan and 50g of red --- and so on... Mix it all up and you have your custom ink. Assuming I could get Red, Green, Blue at the same viscosity first, then thin out as needed. Is there a website or an app that can give me the mixing amounts or is this not how it's done in the paint world? I'm not painting a house. These are small projects like refinishing tables or chairs or mods to my computer. I'm aware I won't be using the same paints for those different applications. I don't need my table to be rust proof. On the other hand if it's just easier than I don't care. I also don't need to be matching 100% to a paint chip at first. I need to be in the ballpark and learn from there.