Sabotaging is pretty simple. All Killers alive can place up to 3 bombs anywhere in the house. 
After you have chosen the perfect place for at least two of them, you can choose between activating them or finding a place for the third one. 

Once the bombs are activated, one of the Guests is needed to complete a task and prevent the explosion. If they fail, you won, suspect!

Also, Killers can deactivate lights to keep everyone from seeing too far from their own spot, which is a great way to hide bodies o.O

To reactivate the lights, a Guest must go to the garage and complete a task. 

While deactivating lights can be performed by dead Killers, placing bombs cannot be performed by Ghosts!
Keep in mind that all sabotages have a cooldown, so use your time wisely!