First off, welcome to the forum!
This is without a doubt the most asked question here.
In fact it has been asked and answered several times just this week.
Have you looked at the post list or searched the forum for "battery hookup?"
Here is a teeny sample of what you can find:
Wiring two batteries together question.
2 battery w/switch wiring schematic
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW