Board Thread:Wiki News and Announcements/@comment-67.171.222.59-20140701102333/@comment-81.129.0.150-20140701144431

You need to wear the jetpack in the chest slot. Electric jetpacks must be charged, regular jetpacks need fuel. Then just jump and up up and away you will go. Press M (default key) while pressing Space to toggle Hover mode on or off, which will give you finer controlover your ascent or descent, also meaning you won't take fall damage when landing (except on SMP servers where the number of ticks/second has dropped significantly).