A gesture is an animation of some sort that a playermodel can access from Garry's Mod. Most playermodels can use all animations. However Pisti's Pony playermodels are different, since they have no pre-existing base in Garry's Mod, our friend, Pisti has to animate the gestures, by hand. So there is a limited amount of gestures.

Currently you can only use the following;
• Dance -- Do a lil' jig
  
• Wave -- Say hi to you friends or signal a helicopter.
  
• Bow -- Kneel for a higher power.
  
• Salute -- Show your respects to higher powers.

• [Recommended] You could open your Garry's Mod console and type:
  bind <key> "act <gesture>"
• You could also just type into your console:
  act <gesture>
• You could use an addon such as this or this

• Gesture Menu & Commands by Tenry can not be used in multiplayer
  
• Nexus Gesture Menu by Nexus [BR] can be used in multiplayer
  
• Typing "act <gesture>" is single use, meaning you have to type it everytime you want to dance
  
• <KEY> CAN BE ANY BUTTON ON YOUR KEYBOARD
  
• <GESTURE> CAN BE ANY ONE OF THE ANIMATIONS