Put your hand out of your window or take a walk outside.
How do you feel on your skin--hot or cold? Is it dry or humid? Does that cloud make you sweat? Does the sun feel good or does it feel too hot? Is it windy today?
Weather is the way the air outside feels to us—hot or cold, dry or humid, sultry or cool, cloudy or sunny. Thunder, lightning, storms, rain, snow, ice, hail—these are all expressions of weather. Weather is always changing and is caused when a lot of little things are put together and react to each other's presence.
Let me give you an example. Say there's a breeze that has been travelling over land for a long time before it reaches you. That breeze will feel dry on your skin. If the breeze comes to you after flying over the ocean or the sea for a while, it will have a lot of moisture and so it will feel damp on your skin.
Here's another example. The sun is shining but you are standing in a wooded area full of leafy trees that form a canopy and stop the sunshine from reaching you directly. Here, the sun will feel less warm to you than if you were to stand in an open field. The sun will feel even hotter if you stand on a sandy desert.
As I said before, weather keeps changing. It was bright and sunny this morning when I left home but now it's really cloudy and it looks like it may rain.
One of the things I really like doing is watching the weather channel sometimes. I like to see those maps and charts of how the weather's going to change from hour to hour, day to day, week to week.