Garry's Mod (GMod) is a sandbox-style computer game that allows players unlimited freedom to create scenarios and simulations. Players can summon items such as weapons, vehicles, explosive barrels, rag dolls and non-player characters (NPCs) to fulfil any of their desires. Buttons in GMod allow any player to activate the mechanism it is attached to. This is helpful when playing on a public server online and you want other players to be able to activate your creation.
Create an item that uses a mechanism, such as hydraulics, thrusters or winches. This must be something that uses the numpad for activation.
Open the creation menu by pressing "Q" and select the "Button" option under the Construction category.
Select the button model you want and set it to the same numpad number as the mechanism from step 1. If you made a hydraulic door and set the hydraulic system to numpad 1, set the button to numpad 1.
Place the button down wherever you desire.
Stand close to the button and press the "Use key (E)" and it will activate your mechanism.