Thank you for looking at this build!

Before I begin explaning, my choices of items and the way I play Rengar, I'd like to tell you that the build is not detailed and it covers the most basic things you need to know to learn the champion really fast.

The gameplay of Rengar is practicly simple:
1. Get in bush.
2. Jump.
3. Kill.
4. Run away!

What do I mean by that? Well, Rengar is a very fun to play champion, he can disrupt fights, take down potentionaly weak champs and get almost every kill. Your skill sequence is as follows:
(Stack your passive for OP dmg ^^)
ATTACKING!
1. If a target is under a tower and you need to take him out quickly (Veigar, Sona....:
(R)>Q>Q>W>E (stacked passive)
2. If a target is under a tower and can escape easly (Singed, Wukong, Irelia, Ezreal....):
(R)>E>Q>W>E (stacked passive)
(NOTE: Using ulti is optional)

RUNNING AWAY!
(NOTE: Your ulti is a great engadgement and escape tool, don't waste it if you can kill a target without it!)
When running away you need to keep track of where your oponents are! Use ulti only if the situation requires it(Example: 1 VS 5). Skill sequence: (R)>>>>>if they are still following then>W(to heal) or E(if you are full hp and you need to snare someone).

So yeah that is basicly what you need to know about rengar.
And remember, every build is played differently ;)