>>3468471Knock on the wall. I'm not shitting you. Around the area where you want to hang it. Listen to the sound. Knock in horizontal lines from a starting point. What you're trying to find here is a stud. A piece of wood that the drywall is attached to. Listen to the sound. You'll be able to distinguish the shallow knock sound of a stud from the deep knock sound of dead air drywall. Once you're certain you've found a stud where the drywall is mark the location.
Find a nail of suitable length and width. Hammer it into the stud about halfway. There should be a piece on the back of the picture like a wire or shark tooth looking thing. Put the head of the nail in there and adjust for straightness. If you have a bubble level you can make it completely level by putting it on top of the picture frame and trying to balance the bubble in the two lines.
Good luck anon I can't explain it any better than that.