I'll open with the famous Dave Grohl's rant:
“When I think about kids watching a TV show like American Idol or The Voice, then they think, ‘Oh, OK, that’s how you become a musician, you stand in line for eight fucking hours with 800 people at a convention center and… then you sing your heart out for someone and then they tell you it’s not fuckin’ good enough.’
Can you imagine?” he implores. “It’s destroying the next generation of musicians! Musicians should go to a yard sale and buy and old fucking drum set and get in their garage and just suck. And get their friends to come in and they’ll suck, too. And then they’ll fucking start playing and they’ll have the best time they’ve ever had in their lives and then all of a sudden they’ll become Nirvana. Because that’s exactly what happened with Nirvana. Just a bunch of guys that had some shitty old instruments and they got together and started playing some noisy-ass shit, and they became the biggest band in the world.
That can happen again! You don’t need a fucking computer or the internet or The Voice or American Idol.”
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Believe in what you can bring to the table
You can begin playing guitar with other people if you can, at least, strum a chord in time and know your very basic chords, like open chords and power chords.
Something even more important is being confident of what you know and being conscious of what you don't know (and want to learn). If you can only play power chords, that's great, Johnny Ramone made a reputation only playing power chords, they even made a statue for him! But you have to be confident about what you know. If you let self doubt prevent you from playing with other people, you will never get in the path to reach your full potential and have some serious fun. Music is a social endeavor, you enjoy it even more when you're playing with someone else.
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Technical advice for any aspiring guitar player
If you still feel like you don't have what it takes, I'll run a checklist (open for discussion and improvement) on skills and knowledge that are helpful when you want to play with someone else:
playing in time - being able to play in tempo and with the beat is the most fundamental skill you need, even if you can play any melodic line, if you can't play in time, you can't play at all
basic chords - knowing at least one way to play all 12 major and 12 minor chords, which means you can play in any key; more "complicated" keys will have more sharps or flats and will require to play bar chords, though
knowing the "classics" of your preferred genre and style -
