Hi, and welcome to posting.
Here are some starters for you. These links have been posted any number of times here.
Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams
This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
1/BOTH/2/OFF Switches Thoughts & Musings - SailboatOwners.com
They come from this "Electrical 101" Topic --- Electrical Systems 101
As you get into the specifics, we can help you some more.