I started playing Magic for about 3 months. I started playing because all my friends were and it seemed really fun. [Which it is.

] I started buying cards and packs when RTR started. So, I decided to build several decks and I'm focusing on three right now. The one I'm really focusing on right now is my Selesnya Deck. Here is what it contains
Artifacts
Tablet of the Guilds x1
Selesnya Keyrune x2
Creatures
Palisade Giant x1
Elderscale Wurm x1
Gatecreeper Vine x2
Centaur's Herald x 3
Trostani, Selesnya's Voice x1
Vitu-Ghazi Guildmage x2
Wayfaring Temple x3
Dryad Militant x2
Enchantments
Cathars' Crusade x1
Collective Belssing x1
Growing Ranks x2
Instants
Fog x2
Druid's Deliverance x4
Heroes' Reunion x1
Selesnya Charm x4
Lands
Grove of the Guardian x2
Selesnya Guildgate x2
Forest x8
Plains x8
Sorcery
Ranger's Path x1
Courser's Accord x2
Call of the Conclave x4
I would really like to compete in FNM tournaments. I attended one [but did not compete] today at my local card shop and it looked really fun. Everyone was having a blast. As for budget, ehh, it depends. My friends and I just kinda give each other cards if we need them, but for now, lets say it's low. I also want to say this deck is legal, but I don't know. I would just like my deck to be able to compete. That would be awesome. Thank you to everyone that helps me out on this. I appreciate it a lot
Well, FNM would probably require a significant upgrade to be competitive. Nothing really crazy unless you want to win 1st place regularly, but it would require some cash layout (or trading, if you're into that). Selesnya aggro decks exist and are reasonably competitive, but at a minimum, you would want:
4x Thalia, Guardian of Thraben
4x Avacyn's Pilgrim
4x Silverblade Paladin
2-4x Loxodon Smiter
2-4x Wolfir Silverheart
2-4x Rancor
and a better mana base. Among these cards, the Silverblades are a significant expense, because a playset will set you back about $36 if you buy cheaply online (and somewhat more if you buy from your local store). They're probably the only reason GW can compete as a deck, though, so they're basically the core of the deck, along with Avacyn's Pilgrim, a mana dork that's a common and thus pretty easy to get a hold of. Rancor is an uncommon, but it's $3 because of how in-demand it is. It has an amazing synergy with Silverblade.
The Thalias are a few bucks each, and also pretty necessary. Smiters and Wolfir are also a few bucks each, but you could probably skate by without full playsets for budget reasons.
You also need to look into deckbuilding basics. You're running only 20 lands now, and that's too few. A competitive Selesnya aggro deck is going to run 4-6 mana dorks (4 Avacyn's Pilgrim + some number of Arbor Elf) and still run 22+ lands. For your mana base, ideally you would have 4x Sunpetal Grove and 4x Temple Garden. The Gardens are still pretty pricey, so you may decide to stick to just 4x Sunpetal in the beginning, but you really can't go lower than that. You need reliable access to G on turn 1, GW on turn 2, and GWW on turn 3.
So yeah, FNM is a bit of an expense if you want to have a reasonably competitive deck. It's possible to build a more budget version of GW built around populate, which can probably win a game here and there. I would imagine it would have a core like this:
4x Avacyn's Pilgrim
4x Call of the Conclave
3-4x Selesnya Charm
2x Grove of the Guardian
2x Trostani
and 0 Fogs/Druid's Deliverance, fogs aren't good in this deck. There's a bad turbofog deck you can make in Standard, but even that would need one more color at a minimum.
...Eh, I don't know though. The more I think about it, the more Populate.dec strikes me as fun for kitchen table magic (it's also great in EDH!), but just... bad otherwise. It has all the weaknesses of GW - it's just a pile of dudes, has 0 reach, and gets pulverized by sweepers. At the same time, it lacks the strengths, which right now is basically the explosive power of Silverblade + Rancor and the ramp into this provided by Pilgrim (beautiful curve: T1 Pilgrim, T2 Silverblade, T3 Rancor & swing for 10). The main thing is, it doesn't do anything very powerful, it just sorta durdles along making 3/3 centaurs.