How to Use Heat Shrink Tubes and Sleeves
The heat shrink tubes are some kind of tubes that is constricted when heat is applied to it. Heat shrink tubes are better than other types of tubes and sleeves because they’re easy to use and fits well.
It can be used in electronics and electricals to protect the exposed parts of soldering, wire connections, protect the leads of resistors and other components etc
The heat can be applied using a cigarette lighter or matches, and the more heat you apply, the more thinner it can become.
The heat shrink tubes are available in several sizes depending on your usage, here is a photo showing different sizes

Image credit: AliExpress
You can cut the tube and insert it into the components that needs protection, then heat it to make it shrink and fit to the part