This is the king of swear words in Algeria. It simply means “Fuck off”
The 9 is used to refer to an arabic letter ق which sound doesn’t exist in the alphabet. The closest sound to it is the letter K so you can just say Kawad.
Samir: Listen, she didn’t mean none of that shit you made up in your head.
Kaz: Yeah right ! I don’t mean to ask you to shut up either.
9elwa is a very familiar name for a part of the male anatomy, in this case a testicle. Going in pairs, the testes are located below the penis and allow the production of sperm as well as hormones. Also used to describe a very powerfull person, or an idiot, depends.