how it works CD is the following.
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CD! so this is the base for the deck, it has 67 card in it, which blows and you shouldn't play it, but it's a base. tell me which cards you like the most and are happy about the most, and i'll work around making it a 60 or 61 card deck. :)
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use lands + birds + arbor elf + llanowar elves + lotus cobra + harrow + garruk wildspeaker to gain mana. you may use the mana generated that turn to get out more things that produce mana (much better earlier on)
after you have sufficient mana, you cast a few expensive spells, which are Rampaging baloths, primeval titan, khalni hydra, bellowing tanglewurm, or to make omnath huge!
so that's all fine and dandy, but it's boring. you've already played that deck. it has no tricks up it's sleeve (though your old one did have one or two i think) this one has a few more. I'll explain each one in detail. and i'll explain a few other things i think might need it too.
KHALNI HYDRA - no one expects a turn 3 8/8 trample. t1=forest, birds, t2 = cobra, tap-sac land, cobra, t3 tap-sac land, float green mana, two cobras + a tapsac = 4 mana, not to mention the other previous lands, not to mention your birds. :)
BELLOWING TANGLEWURM - well, since you have all green creatures... bellowing means that none of your creatures can be blocked. isn't that just mean........... ;)
ASCETICISM - obviously you know the card, but you'll always have enough mana to use it, and it means that you can always keep your creatures alive through damage, burn spells, bounces, and kill spells.
MISTY RAINFOREST and VERDANT CATACOMBS - basically there for landfall only. say on t4 you play a baloths, the tap sac land means that instead of getting a single 4/4 token on the field, you're getting an extra for 1 life, not to mention it works the same way with lotus cobra. :)
GARRUK WILDSPEAKER - garruk is nice for a few reasons, firstly, he lets you add more mana by untapping more lands, secondly he'll buff up your creatures with his -4 ability (see below for a plainswalker introduction)
FLING - you have 1 mountain in your deck, but 4 birds, and cobras can produce whatever kind of mana they want... basically the card works like this. at instant speed (so at the end of their turn, whenever they tap out, whenever they almost kill something of yours, you cast it,) anyways. at instant speed, you sacrifice a creature, then deal damage equal to it's power to a player. say omnath is a 20/20 and you're opponet is tapped out. auto-win. :)
HARROW - pay 3 mana, to sac one land, and bring two on the field, but they enter untapped. not bad, especially for landfall cards. :)
GENESIS WAVE - oh, probably one of my favorites in here. say you have 30 free mana, which won't be uncommon REALLY, you genesis wave for 8 (meaning you pay 11 for it) and you look at the top 11 cards of your library, and play any of them you want. say it's 3 primevals and 4 baloths, then 4 tapsac lands. well, the card doesn't say what order, so it all goes off simulationiously. you lay down 4 baloths, that's 4 6/6 tramples, then 3 primevals (so search 6 lands entering after baloths, so total 4 6/6 tramples, and 6 4/4's) then come 4 tap sac lands, they enter untapped, so pay 4 life and get 8 more lands. that's 4 6/6 tramples and 14 4/4's. oh joy. unless they have a day of judgement, you win. :)
GREEN SUN - need i say more? just know when to time it right on getting a power card or a shit card.
planeswalkers - see bottom right? there's a number, garruk has 3. it's the loyalty counters he starts out with. when he comes into play, you can use one of his abilities, so long as he has the loyalty counters for it, some abilities cause him to gain counters, some lose. for instance. he enters for 4 mana, then you can untap 2 lands. :) fun, right? :) or you can make a 3/3, you can only use the abilities once per turn, and they are sorcery speed, meaning that you can only cast during your main phase 1 and main phase 2. :) he's pretty good, and godly in green + other colored decks, b/c you can choose which land you untap. :)