New to Rengar

As the title says. I’ve been having a lot of fun on Rengar as someone new to league. He looks awesome and his play style seems really cool so far. So I ask what are some tips yall can give me to get better on him. How do I build him effectively (runes and items)?, What should be my goal in a game?, How do I know if I’m stronger then an opponent I want to jump?. I would appreciate any and all help I can get.