Donna, many thanks for the question. Before trying to answer it I thought I would ask my team a question.
Donna, what do you think about the puddles question? Think about how you would answer it and then go to my answer to a previous question.
Now to your question. Firstly I have created a little animation to show how the puddle disappear. You have to imagine that the shapes are water particles (molecules is the proper word). In the puddle they are all moving around. Most of them like being with the other particles BUT some are just moving around a little bit too fast and manage to escape from the puddle. When the Sun begins to warm the puddle it makes more water particles move around faster and more escape. This goes on until the puddle disappears.
At home look at the steam from a kettle, BE VERY CAREFUL AND CONSULT AN ADULT. At the exit of the kettle spout you can see nothing, BUT just above this the hot water particles begin to cool down and slow down and reform clouds of water.