Want to know more about Ninetales in the game? This is the page for you.
Each Pokémon has base stats that determine how powerful it is. These stats go on to influence many other aspects of a Pokémon's capabilities. Ninetales's base stats are as follows:
Special Attack: 81
Special Defense: 100
Ninetales isn't in the top percentile of Pokémon, stats-wise, but its Special Defense and Speed are nothing to scoff at, and if augmented properly with EVs, Ninetales can withstand a lot. See the strategy section for more tips.
Ninetales's usual ability is Flash Fire. This prevents Ninetales from being damaged by Fire-type moves, and, once a move has been blocked, Ninetales's Fire-type moves do 1.5x damage until it leaves the battle. Unfortunately, you won't often find opponents who use Fire-type moves against Ninetales on purpose, so this ability isn't very good.
Generation V introduced Hidden Abilities, which you can get through a variety of methods; Bulbapedia has more information if you're interested. Ninetales's second ability is Drought, a far more useful option (and previously only available to Groudon, and later also Mega Charizard Y). Drought changes the weather to sunny. If a Pokémon with Drought is sent out at the same time as a Pokémon with another weather ability, the Pokémon with the slower speed's ability will activate.
In Gen V, it lasts indefinitely unless cancelled by another weather move; in Gen VI it lasts only five turns unless the user is holding a Heat Rock, which will change it to eight turns.
Ninetales evolves from Vulpix through the use of a Fire Stone. Like many Pokémon that evolve through the use of a stone, Ninetales learns no moves on its own; if you want to teach it anything, you need to use a TM. (Generations II and III are the exception to this; Ninetales could learn Fire Spin at level 43 and 45, respectively, but this changed in the later generations.)
There are many different locations to find Fire Stones in the games; in some generations, you can buy them in stores; in others, they're given to you by certain people. Bulbapedia has a full list of locations for all your Fire Stone needs.
Of course, you'll need a Vulpix first. veekun's breakdown will get you a Vulpix in no time. (Vulpix can't be caught in Gen VI — it needs to be bred from a Ninetales caught in a Fire-type Friend Safari.)
Ninetales and Vulpix are part of the Field egg group, which gives them a decent number of Pokémon to breed with. Personally, I don't find breeding all that important with Ninetales; most of its good egg moves are — at least by Gen VI — moves that it learns by level-up, or can be taught by TM. Hypnosis is the only move of note that it doesn't learn by level-up.
There are many good move lists out there for Ninetales, so I won't bother copying one here. I personally recommend veekun for the many options it has. You can find a link to Ninetales at other Pokédexes at the bottom of that page.