Hextech Crafting is confusing to me. Please Help.

Okay so I earned two S's on my lvl 5 champ and want to go to level 6.

I already opened my chest for that champ; I had no idea what I was doing.

Anyway, now I need a Champ Shard or a Permanent.

I already have a key, do I need to BUY a chest? And if so, will my chances at a Shard or Permanent be completely random??

Thank you.