All you pretty much need is a Pokemon Trainer Club account and you'll mainly be using the "My Play! Pokemon" page.
Events:
Find an event near you and attend it, use the
Event Locator for this. The times stated are registration times and can usually last up to an hour.
For registration and player ID:
Now during registration you'll be asked for info which will include your Player ID. This can either be given to you at the event or you can get your own online through your Pokemon Trainer Club account. If it was given to you at the event, you'll have to add it on to your Trainer Club account (I think, imo it's better if you just get it online). It's easier to have it noted down because you never know whether your signal is good or bad, but it's the first thing listed on your My Play! page when you log in.
Here are the
VGC 16 rules just in case.
Only things not included are:
- Bring 6 choose 4.
- Automatically leveled
down, to 50. <- Will not level up to
Pretty straightforward so the battles you can pretty much jump in to.
Now for the actual event:
You start off with single round swiss and the number of swiss rounds usually depends on participation. Then there is a top cut, a best two out of three rounds bracket tournament for the top players (the ones with the best swiss records) at the event. The number of players allowed in top cut also depend on participation.
And finally on to prizing:
It depends on who's hosting it. Most of the time at the Premier Challenges, you'll get plushes, gift cards, figurines, amiibos, cards, etc. Regionals give out even larger prizes such as 3DS systems and trophies. Then you have Nationals and Worlds..