To improve is to get better at some activity. You may already know the meaning of this word, but pay attention to the way "improve" is used with other words in the examples below:
Practice improves performance.
Rachel improved her guitar playing.
Antonio has improved as an artist.
The woman who had a heart attack a few days ago is improving.
How can you improve your English?
You can improve your English by practicing it every day.
My students improve their English if they study every day.
The city has improved its transportation system.
Scientists have been improving their knowledge of how to cure diseases.
The U.N. tries to improve living conditions for people around the world.
The word "improvement" is a noun.
He made a big improvement in class today.
The teacher grades on improvement.
She has shown a lot of improvement as a student.
Your improvement has been remarkable!
His health hasn’t shown much improvement.
Improvements in the neighborhood lead to a decrease in crime. (This sentence uses "improvement" as a count noun.)
They’re doing a lot of home improvement right now.
He’s made a lot of improvement as a speaker.
The word "improved" can be used as an adjective:
An improved surface will be easier to drive on.
New software for our computers resulted in improved performance.
Note: Sometimes you’ll hear the verb "improve" used with reflexive pronouns. This might sound kind of strange at first, but it’s okay. This usage indicates that a person is doing something in order to become a better human being or a better student or a better you-name-it.