So we see lots of people with jetpacks in Star Wars (okay maybe not mostly just Jango and Boba Fett but still) but they never explained how they are used. We never see them press a button to use their jetpack. So how are they used?
Wrist and hand controls
According to Galladinium's Fantastic Technology, a Star Wars roleplaying game supplement (and thus Legends):
Wrist or hand controls adjust the angle and pitch of both input and exhaust vanes, allowing for both vertical and horizontal flight.
—Galladinium's Fantastic Technology
This applies more specifically to Jango Fett's jetpack, but presumably other jet packs had similar features.
The main control console was located on one of Jango's forearm panels. However, it often happened that Jango had his hands full (of weapons) when he needed to ignite the jets, and so a verbal control interface was included in the bounty hunter's helmet. With just a word, Jango could be up and away.
—The Official Star Wars Fact File #60