In Hello Neighbor 2/Hello Guest, there are many items you can use. This page lists the functions of those items.
Shop Items (Hello Guest Alpha 1)
The Flashlight is a bulky black item with a handle. It emits a light with left click which you can disable again with left click. Be careful, if the flashlight is on too long it can go out.
The Thermos is an item used for stress. It is a yellow canister with the name "eet" printed on the front. In Hello Guest Alpha 1, stress makes your camera shakier. If you drink the thermos, it is consumed and cannot be used again, but it reduces your stress meter.
Need to power something? Get a generator. If you turn it on and hook wires up, it can power certain things. You will require a certain amount of wires for whatever you are powering. The generator is a box in the shop with a yellow triangle on it. In the map, you can hold left click to place it, which shows a red and blue generator with a lever and triangle printing once placed.
The electric cords are blue and red wires wrapped around a gray thing for storage. You can connect these to the generator to power things. Left click on the generator's socket and make sure you are in the range of another socket in the map, then left click that.
The rope can be used to descend from places safely. If you are high up, left click on a nearby wall or railing and jump down. To exit the rope while suspended, press space.
The lamp is used for scaring the Guest, but it does not function properly in Hello Guest Alpha 1. It can be connected to the generator due to its socket which is how you power it up.
The camera is a useful item. It is a blue camera with a green light. It can help you track vandals and the Guest. Left click to place it on a wall. Be careful, once you place it, its battery starts going down. To use the camera, you will need a monitor.
The monitors are beside the cameras in the shop. They look like tablets and are green. Once you place your camera, left click with the monitor out to control it. You can zoom in on cameras with W and S and switch between your placed cameras with A and D. (In Hello Neighbor 2 Alpha 1 and Alpha 1.5, there is a limit of 4 cameras.)
A useful item. It is a red barrel with a black tube at the top. If you look down, jump, and hold left click, the Fire Extinguisher lets you fly to a decent height. Be careful, as this can run out if used too long.
The Battery can recharge the cameras and flashlight. If you left click one with a battery out, it restores its power.
The Gas cans are red cans with a fire logo on them. They are used to recharge the generator. Press left click on a generator with a gas can to charge it.
Crafted Items (Hello Guest Alpha 1)
More will be added...