slide down: in a tab, when it says something like e| ---6/5--- for one of the strings, you hold down the sixth fret, strum that string, and while still pushing down slide your finger to the fifth fret. It's the opposite for slide up.

Harmonics: put your finger above the 5th, 7th, or 12th fretwire, and lightly touch the string. pluck the string, and as it begins to ring pull your finger off so it resonates. if it makes a dead note noise, try moving your finger around or adjusting finger pressure
All the others look covered...
well i do just fine, my car and my guitar, guitar GUITAR!