I'm following along an Umbraco tutorial series but I don't really understand what Models and Models Builder are and the different modes for Models Builder. I come from the React world and Nodejs, and I'm very new to everything .NET and MVC.

Check out https://docs.umbraco.com/umbraco-cms/reference/templating/modelsbuilder/configuration Also i posted a similar question 4 days ago in this area called "need clarification on modelsbuilder" that might help as well.