Use a strap. Always use a strap.
Review the GT lessons that teach posture and position but understand...
...a strap will solve most issues about holding the guitar and will keep the instrument stable.
Good luck, have fun.
"It takes a lot of devotion and work, or maybe I should say play, because if you love it, that's what it amounts to. I haven't found any shortcuts, and I've been looking for a long time."
-- Chet Atkins
-- Chet Atkins