New Rengar Please Help

I do not even know where to start, I feel like whenever I play with Rengar I have 2 options: or I'm playing passively, farming and doing nothing and losing the whole thing of Rengar or going for ganks and making nothing happen. I am lost, I never had so much frustration trying out a champ, and I played a lot of high-ceiling champs, but he is special something doesn't click with me although I love his game style a lot