Get a teacher. If not, at least watch A LOT of technique videos. don’t hurt your hand. it is very easy to hurt your hand. Don’t practice until it hurts, especially if you’re not sure if your position is ok. There’s a book called the abcs of bass for the absolute beginner. it’s a kids book, but i learned with it as an adult. good to get you started with some beginner songs while you complement with etudes for technique from a Simandl or similar book.