In my last game, I got reported for learning 
and inting. I just bought him a day ago and trying to learn him. A teammate said that I should learn all his combos immediately and play like a pro or i get reported. :/
No.
Even if you have 28K games and 750K mastery points on Renekton, it's not punishable to be bad at the game, as long as you're not losing on purpose. Anyone can report you for anything, false reports don't matter.
It would be a d1ck move to take the first game on a new champion into ranked but in normal games it should honestly be fine. You get better through practice after all.
I played renekton in unranked
I'd only hope for you to be punished if you were playing a new champion in ranked and fed hard. In normals, who cares? There really isn't a better place to learn than in normals.
Who gives a shit if you get reported? Unjustified reports do nothing. You gotta learn new champs somehow, and bots are bullshit.
If you first time and learn in norms thats fine. Even if it may suck to have someone int me because their learning as long as its not ranked i don't mind too much. I don't play renekt but i could try and recommend some stuff
Go to U.GG for champion guides and all that
i suggest 
>
>
With the rest depending on how the game is going.
Runes being either Conquerer or PTA with triumph> bloodline/alacrity> Coup de grace/ last stand> domination > sudden impact> Eye ball colection. attack speed stat> adaptive force> armor/ Mr depending on what you need. If im wrong please down vote and correct in comment thingy.
