From Second Life Wiki
Gestures are a combination of animations, sound clips, and chat text that are played as a group automatically. They can be triggered when active with a short text string in chat, a keyboard shortcut, via this window, or the bottom toolbar "Gestures" button. Any gesture, active, or no, can be triggered when open for edit.
This window shows the currently active gestures from your inventory. It is opened by menu itemEdit > Gestures... or Ctrl-G keyboard shortcut. Gestures can be activated/deactivated by finding them in your inventory window, right-click for context menu, then choose "Activate" or "Deactivate".
Active gestures may be sorted by Trigger, Key (shortcut), or Name. Double clicking any item will play the gesture. Clicking the "New" button will open the "Gesture" floating window, and create a new item in your inventory called "New Gesture"