As part of the hydrological cycle, water is evaporated off of the surface of the earth and turns into the gaseous form of water which is water vapor. With temperatures getting colder as you go higher, the water vapor will begin to condense into water droplets in the process called Condensation.
As this happens, the water droplets will come together and begin to form clouds. This will continue till the cloud gets too heavy for the capacity of the atmosphere and will then fall as rain.
If you're apart of K12 public online school and you're doing this lab report you can find the PDF for the common leaves sheet of the 10 leaves in 3.03 Dichotomous Key Investigation: Dichotomous Key under Materials then you just look at the example and instructions and fill out that way