This is a simple demonstration to show how clouds form.
All you need is a a clear plastic 2-liter bottle, water and a match.
Remove any labels on the bottle so you can see through it.
Fill the bottle about 1/8 of the way with warm tap water.
Light a match and allow it to burn for a moment before dropping it into the bottle. It will extinguish when it hits the water. Cap the bottle and squeeze the bottle with both hands.
Release the pressure and see the cloud form in the bottle.
When the pressure is released on the bottle, the air inside expands, and therefore cools (adiabatic cooling), causing condensation. "The vast majority of clouds that you see are formed via adiabatic cooling." (Exploring Creation With Physical Science, Wile)
The match put small particles of smoke in the bottle, allowing something for the water to condense on, causing the cloud. Actual cloud water droplets are typically formed around dust particles and soot from wildfires. (source)
source: Exploring Creation with Physical Science, Jay Wile