Press E to interact with the NPC in front of you and use numpad keys to go through dialog.

There is 4 buttons on the vending machines (Red, Yellow, Blue, Green) which give you different sodas. The elevator has 3 buttons, the top button calls it up, bottom one calls it down, and the middle can send it up or down. The green button near the dummies enables/disables their ability to randomly move around. All starting tools have a form of functionality upon clicking.