Do I HAVE to hit them in oder to play a song right? (Smells like teen spirit)
My friends and a couple people told me they're optional. I DO wanna wanna play them if Kurt did but not if he didnt.
They are dead notes - you mute them (with your fretting hand) to play them, so it makes a percussive noise rather than a proper note. If you miss them out then the song will still work but it might sound a bit bland, especially rhythmically.
Are they single dead notes, or are they dead chords?

For single notes just touch the string with a bit of spare skin on your fretting hand, and pick it like normal - with practice it will sound ok.

When its chords it can be a bit harder as there are so many natural harmonics on a guitar, so its hard to deaden it without getting either harmonics or some of the notes ringing out, but its just practice. The more you do it the easier they get. If you can't play them very well yet, all the more reason to use them as practice makes perfect
Quote by RAAAGE
I know what they are but I can't play them good at all.

As has already been said you can leave them out but they are an integral part of the make up of the song so it won't sound to good, why not practice mutting then will have learnt a new and very usefull technique, you will never learn to play if you dismiss basic tecniques like this just practice it.
I wish I had tallent and ability.

Squier Vintage Modified Strat, Black with laquered 70s neck
Farida FLP-26
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Ampkit for iPod
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