To pass through a door, click on it and select "Pass Through" like:

All doors lead to different locales.

Special machines that you will certainly come across inworld are vendos (vending machines) that sell items to you. Vendos come in all shapes and sizes. Some vendos are squared/rounded (like Variations), some circular and some actually look like the item they are selling (spray can vendos). To use a vendo, click on one and you will be presented with a menu of options:

"View Next/Previous Item" lets you scroll through the items for sale and "Buy This Item" lets you buy the item currently shown. If the vendo is a stand alone (looks like the item for sale) then just click "Buy This Item" if you want it (View options will not be availible).

If you buy an item that you decide you no longer need, you can pawn the item for a fraction of the price it was in the vendo. To pawn an item, hold it in your hand and click on a pawn machine:

"Appraise" will tell you how much that item will pawn for and "Sell Item" will actually pawn it. Just incase you hadnt already guessed, once an item has been pawned, it cannot under any circumstances be recovered.

Some items are useable in other ways... click around and experiment for yourself!