The word "concentrate" is usually used as a verb in everyday speech. One example would be the sentence "I quit my afterschool job so I could concentrate on studying," or "A basketball player must be able to concentrate under pressure in order to make important free throws." In this sense, the word means "to focus one's energies on a task."
When used as a noun, "concentrate" usually refers to a chemical or substance that is simplified or reduced down. An example of this would be "The chemical reaction required a concentrate of the substance," or, in cooking, "The orange juice was made from concentrate."
This is a great question.
Concentrate is usually a verb with a number of meanings. The most popular meaning is the idea of thinking intensively. So, we can say: "The boy must concentrate if he is going to learn the difficult material." Another usage has the idea of bring something into one place. An example would be: "New money is concentrated in many modern cities."
Concentrate can be a noun in certain contexts, such as mining. For example, when rock is taken out of some ore, we can talk about concentrate as a noun. In this context we can talk about a mineral concentrate. However, apart from this context, the noun form of concentrate is "concentration."