This is only for parts of the game you can interactive with that cannot be picked up.
Open them to go into a room.
Code doors require a code to enter a specific room. These are most evidently found on notes. (Example: Dr. Klark's room which requires the Code found in SCP-106's Pocket Dimension.)
These are of course, computers. They contain conversations, messages, and/or text logs. Some include log-in passwords such as Dr. Klark's computer, but other computers such as Dr. Coog's (outside SCP-895) are freely accessible(Because Coog was silly enough to forget to log off).
Key Card Holders
These are simply holders you need the Key Cards to get in. The colour of the holder depends on the level of the SCP and the according card is needed.
Drawers are easily opened by clicking on them. Almost all of the time, nothing is inside, but be aware - something very important might be hidden inside!
The Vending Machine allows you to insert a coin and get a snack! Simple, right? Just remember to bring money. Coffee Machine-- The Coffee Machine is free to use, giving you a nice, hot cup of coffee with great deals of caffeine.