Hi and welcome to the hobby
First off I wouldn't recommend any sort of tournament play until you are more familiar with the rules. (particularly as you haven't mentioned owning a codex)
So purchase the codex at the very least and the rulebook if you can afford it
Best thing to do is find a few like minded individuals (maybe friends who are starting the game or people at your
FLGS) and have a few smaller games with them to teach you the rules
Use these games to work out how you would like to play your orks...you can be super competitive, in which case there are plenty of army lists on the internet. Or you could prefer something a bit more exciting like a speed freaks fluffy list.
This way you can steadily build an army you enjoy playing and which is suited to your playing style.
Explosivo111