Pre-release are little events that are held before a set comes out. Basically after everyone has registered and paid etc. the tournament organizer will give out everyone 6 packs of the new set (in this case you'll get 6 Phantom Forces packs).
From there everyone has about 30 minutes or so to make a 40 card deck (not the normal 60) out of the cards they obtained. You will have to bring your own Energy cards, however some events may have some you can borrow for the event.
When the times up, the TO (tournament organizer) will shortly post up papers showing everyone and their pairings (who they're against). When these are put up they'll announce it to everyone and you go check your table number and your opponent. Then you go find your table and wait for your opponent to turn up and for the TO to tell everyone they can start playing.
In prereleases you lay with 40 card (as explained earlier) so you'll also only be playing with 4 prize cards.
When all the rounds are over (depends on the amount of players that turned up) the TO/judge will then call up each player to collect their last 2 packs and anything else that you get at the prerelease (at old ones they gave out sleeves and deckboxes but I'm not sure if they do them anymore). You don't get anything extra for winning so the tournament is all in good fun.
When you're playing the game it's best to tell your opponent what you're doing. If something confuses you or you want to see what a card does that your opponent just played, politely ask them if you can check it or ask about the ruling/play you were confused about.
If you have any other questions let me know. Prereleases are great events to start off with. My first event was a PR too. They aren't really serious because there's nothing to lose when you play in them, so it's a nice environment to start off in.