Pokemon Team Help

I haven't played pokemon since ruby and I never really played battled. I want to get into competitive battles for pokemon x and y. I know there is a lot to learn and I have been looking up information and watching some competitive battles. I am playing through pokemon x for the first time and I decided to make a team to battle. This is my team so far and any input or advice would be nice. I still need one more pokemon for my team any suggestions would be nice!

Pokemon Team

Charizard lvl 46
Ability: Blaze
Moves:
Flame Burst
Fire Fang
Wing Attack
Dragon Rage

Golurk lvl 46
Ability: Iron Fist
Moves:
Magnitude
Shadow Punch
Dynamic Punch
Mega Punch

Gardevoir lvl 45
Ability: Trace
Moves:
Magical Leaf
Dazzling Gleam
Psychic
Thunderbolt

Gabite: lvl 41
Abillity: Sand Veil
Moves:
Dig
Shadow Claw
Aerial Ace
Dragon Claw

Greninja lvl 46
Ability: Torrent
Moves:
Smack Down
Water Pulse
Water Shuriken
Surf

I am still leveling up my pokemon and teach them some moves that I cannot get till later on in the game. Also was thinking of adding either Gengar, Mawile, Conkeldurr, Aggron, or Skyamory not sure what pokemon I should use.

In-game teams generally don't make for good competitive teams. Natures, EVs, and items are important parts of competitive battling. I'll give you sets for what your team members should look like, so you know what to eventually go towards.

-Charizard w/Charizardite X
Nature: Adamant/Jolly
Ability: Tough Claws
EVs: 252 Attack, 252 Speed, 4 HP
Moves: Flare Blitz, Dragon Claw, Earthquake, Dragon Dance/Swords Dance

-Golurk w/Leftovers
Nature: Adamant
Ability: Iron Fist
EVs: 252 HP, 252 Attack, 4 Sp.Defense
Moves: Earthquake, Shadow Punch, Drain Punch, elemental punch

Note that those last few moves can only be taught to Golurk on Black 2/White2.

-Gardevoir w/Leftovers or something
Nature: Calm
Ability: Trace
EVs: 252 HP, 252 Defense, 4 Speed
Moves; Moonblast, Will-o-wisp, Wish, Protect

or

-Gardevoir w/Gardevoirite
Nature: Timid
Ability: Pixilate
EVs: 252 Sp.Attack, 252 Speed, 4 Sp.Defense
Moves: Moonblast/Hyper Voice, Shadow Ball, Focus Blast, Psyshock

-Garchomp w/Yache Berry, Haban Berry, or Roseli Berry
Nature: Jolly
Ability: Rough Skin/Sand Veil
EVs: 252 attack, 252 Speed, 4 HP
Moves: Dragon Claw, Earthquake, Swords Dance, Stone Edge/Fire Fang

or

-Garchomp w/Choice Band or Choice Scarf
Nature: Jolly
Ability: Rough skin/Sand Veil
EVs: 252 Attack, 252 Speed, 4 HP
Moves: Dragon Claw, Earthquake, Stone Edge, Fire Fang

-Greninja w/Life Orb
Nature: Hasty/Timid
Ability: Protean
EVs: 252 Sp.Attack, 252 Speed, 4 HP
Moves: Hydro Pump/Surf, Ice Beam, Dark Pulse, U-Turn/Grass Knot/Extrasensory

If you got any questions, feel free to ask.

Looks like an in-game team to me. You need EVs and natures.

Anyway:

The charm that comes with using Charizard is that your opponent will never know what Mega form you're using until you actually Mega Evolve:
-Dragon Dance
-Flare Blitz/Fire Punch
-Dragon Claw/Outrage
-Earthquake/Roost
Nature: Jolly/Adamant
EVs: 252 Atk/4 Def/252 Spe
Item: Charizardite X
Ability: Blaze

or
-Fire Punch/Earthquake
-Dragon Tail
-Will-o-Wisp
-Roost
Nature: Jolly
EVs: 248 HP/84 SDef/176 Spe
Item: Charizardite X
Ability: Blaze

or
-Fire Blast
-Solar Beam
-Focus Blast/Dragon Pulse
-Earthquake/Roost
Nature: Mild/Hasty/Modest/Timid
EVs: 4 Atk/252 SAtk/252 Spe
Item: Charizardite Y

Golurk is rather...mediocre. It's just a worse Aegislash, IMO. If I were you, I'd replace it with Gengar or Aegislash itself. Don't bother with Mawile or Aggron at this point, since you already have a Mega Pokemon in Charizard:

Gengar:
-Shadow Ball
-Sludge Bomb/Thunderbolt
-Focus Blast
-Destiny Bond
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Life Orb/Focus Sash

or
-Substitute
-Shadow Ball
-Disable/Will-o-Wisp/Pain Split
-Will-o-Wisp/Disable/Focus Blast
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Life Orb/Black Sludge

Aegislash:
-Shadow Ball
-Sacred Sword
-Shadow Sneak/Iron Head
-King's Shield
Nature: Quiet
EVs: 240 HP/252 SAtk/16 Spe
Item: Leftovers

or
-Shadow Ball
-Sacred Sword
-Shadow Sneak
-King's Shield/Iron Head/Pursuit
Nature: Quiet
EVs: 244 Atk/252 SAtk/12 Spe
Item: Life Orb/Spooky Plate/Spell Tag

or
-Swords Dance
-Shadow Sneak
-Iron Head
-Sacred Sword/Head Smash
Nature: Adamant
EVs: 4 HP/252 Atk/252 Spe
Item: Life Orb

or
-Swords Dance
-King's Shield
-Shadow Sneak
-Sacred Sword
Nature: Adamant
EVs: 252 HP/252 Atk/4 SDef
Item: Leftovers

or
-Autotomize
-Shadow Ball
-Hidden Power (Ice)
-Sacred Sword/Iron Head/Flash Cannon
Nature: Rash/Modest
EVs: 88 Atk/252 SAtk/168 Spe
Item: Life Orb/Weakness Policy

or
-Shadow Ball
-Pursuit
-Toxic
-King's Shield
Nature: Sassy
EVs: 252 HP/4 SAtk/252 SDef
Item: Leftovers

Outside of the Mega slot, Gardevoir is outclassed by Alakazam, but it does make a neat Choice Scarf user:
-Moonblast
-Psyshock/Shadow Ball
-Focus Blast
-Trick/Healing Wish
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Choice Scarf
Ability: Trace

Otherwise, use Alakazam:
-Psychic/Psyshock
-Shadow Ball
-Focus Blast
-Hidden Power (Ice/Fire)/Dazzling Gleam
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Life Orb/Focus Sash
Ability: Magic Guard

Garchomp should look like these. Aerial Ace isn't worth it, unless you're using it as filler in-game:
-Swords Dance
-Outrage/Dragon Claw
-Earthquake
-Fire Fang/Stone Edge
Nature: Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Life Orb/Lum Berry/Yache Berry

or
-Outrage
-Earthquake
-Fire Fang/Stone Edge/Fire Blast
-Dragon Claw/Dual Chop
Nature: Jolly/Naive
EVs: 4 HP/252 Atk/252 Spe
Item: Choice Band/Choice Scarf

or
-Stealth Rock
-Outrage/Dragon Claw
-Earthquake
-Fire Blast/Toxic
Nature: Impish
EVs: 252 HP/252 Def/4 SDef
Item: Leftovers/Rocky Helmet
Ability: Rough Skin

Greninja is only good with the Protean ability, which lets it apply offensive pressure on the opponent:
-Hydro Pump/Surf
-Ice Beam/Dark Pulse
-Extrasensory/Dark Pulse
-U-turn/Hidden Power (Ice/Fire)/Grass Knot
Nature: Naive/Timid
EVs: 4 Atk/252 SAtk/252 Spe
Item: Life Orb/Expert Belt
Ability: Protean

or
-Spikes
-Hydro Pump/Surf
-Ice Beam
-Extrasensory/U-turn
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Life Orb/Focus Sash

The last slot can be taken by Skarmory, which can support the team by providing entry hazards:
-Whirlwind
-Roost
-Stealth Rock/Spikes/Brave Bird
-Defog/Brave Bird
Nature: Bold/Impish
EVs: 252 HP/252 Def/4 SDef or 252 HP/16 Def/240 SDef
Item: Leftovers
Ability: Sturdy

or
-Spikes
-Whirlwind
-Roost
-Taunt/Brave Bird
Nature: Bold/Impish
EVs: 252 HP/184 Def/72 Spe
Item: Leftovers/Rocky Helmet
Ability: Sturdy

I posted my in game team because I want to eventually use it to battle. I know I have to switch up a lot of the moves since some of them are just for in game filler until I can unlock other moves. I just needed input on how I should set it up. I'm playing through the game once just to get a hang of the pokemon and figure out which ones I like and are good. I don't really know any of the pokemon from platinum, black and white, and the new ones introduced in x and y. I am gonna play through it a second time but that time I am going to properly raise my pokemon and start breeding them. Thanks for letting me know still got a long way till I can properly battle.