A teacher,friend,Instructional video or a beginners book.
If you've never played guitar before, then it will take you a week at least to play things like 'Twinkle Twinkle', a month for playing a simple Nirvana song , a year to play some full Metallica tunes... and years to play stuff like Steve Vai, Malmsteen , Satch , Jason Becker ,etc.
The most important question is what kind of music do you want to play on your guitar?