So you want to play children's card games

>What you need to play
http://www.pokemon.com/us/pokemon-tcg/play-online/download/
Also available on iPad

>How do I get cards?
-It's like handheld card game vidya where you start with almost nothing and work your way up. No Pay to win because you can't put actual money in unless you're canadian or you buy tournament tickets.
-Fight the Trainer Challenge AI to earn some packs once you hit 4 stars on all of the characters.
-Fight an arbitrary number of times with the basic decks and unlock some staple trainers and cards to use in your real/important decks
-You can scan codes from IRL card game products like decks and packs to get them in-game.
-If you get tradable packs, we urge you to save those and trade them for what you actually want. Packs are currency on PTCGO for the trading section, you don't want to gamble away your theoretical money on 6 Krabby and a shitty holo rare that doesn't do anything.

>Tournaments?
-Three tournaments are available 24/7 (Standard, Unlimited, and Theme formats)
-Weekends occasionally change one of 'em to a 5-ticket fee tournament (with formats changing every week). You can find the prize structure in the TCGO client when they're available.
-Tournaments which take tokens to enter usually have Tournament Tickets as prizes
-Tournaments which take tickets to enter usually have tradable packs as prizes

>Formats?
-Unlimited is "use any cards from forever"
-Theme Deck format should be obvious, you go in with a theme deck, fight other theme decks
-Standard uses set rotation, anything before Boundaries Crossed is illegal unless it's been reprinted in a set after boundaries crossed. Full list http://pokegym.net/forums/view.php?pg=stdformat. You could also just check Pokebeach and look through all the sets from Boundaries Crossed up, if you find a card you want to use while browsing, it's fair game

>There's something about Challenges
-It's some recently added thing on PTCGO, basically do what it says and get XP and a prize
-Reaching higher levels gets you more challenges to choose from with better prizes, including packs of cards
-The Theme deck format is your friend when it come to Challenges!

>I encountered a bug/Crash!
A lot of the time the only answer to this will be that PTCGO is a really shitty program. Either restart the client to see if that fixes it, or do a fresh install. Fuckups happen more commonly when there are updates for new sets.

>General Advice
-Quit now while you're ahead
-Start your game off right by entering flashfire, furiousfists, and phantomforces into the "Redeem Codes" screen. It'll get you 3 copies of the Rallying Cry deck which is both fun to play and includes some decent cards for use in expanded and 4 Double Colorless Energy, used in a lot of decks, yours free.
-eBay usually has the best prices on standalone code cards. Check your local card shop. Code cards are only like 15-25 cents each.
-If you want to purchase things that aren't code cards because you like having a bunch of cards instead of just garbage (basic guide for theme decks) see
http://pastebin.com/dehnDD4v