Probably the most common alternate tuning in guitar is drop D. To do this, we simply take the low E string and lower it down a whole step to a D, done easiest by matching it to your fourth string (D). Just pluck the low string first, then the fourth string and slowly lower the pitch of the sixth string until it matches the fourth. As you notice from the video, this drop D tuning gives us some really cool power chord voicings with just one finger which was all the rage with bands like Nirvana, Soundgarden, Alice in Chains, and many other grunge era bands.
As I stated earlier, the vibrato is the most difficult aspect of this performance. In the video I offer two techniques suggestions to approach the vibrato used on this line: the first is placing my thumb over the top of the neck to really get some nice leverage on the string, really treating it like a large band; the other is similar to what Eric Clapton does when he vibratos a note, using my whole forearm to pull the string. I often can't decide on which one to do! Lately I've been preferring the Clapton method with notes like this. Please experiment with them as they're both very useful.