Tomb Raider Classics
In the Classic Tomb Raider Games and Lara Croft Tomb Raider: The Angel of Darkness it was used for picking up items, for using levers and switches, for grabbing hold and for shooting weapons, when drawn.
Tomb Raider Legend, Anniversary, Underworld
Interact is used for various actions such as kicking, moving or picking up objects, for speeding up other actions like climbing, shimmying, diving and more. Occasionally Lara is about to lose her grip when e.g. hanging on a ledge. To prevent her from falling, the player must use Interact to perform a saving grab.
A special icon appears on the screen, when Interact should be used. This helping feature can be turned off in the game menu.
Tomb Raider (2013), Rise of the Tomb Raider
In the reboot games the action button is used for a variety of interactions like using a torch to burn down a barrier.