use
To make something do a job or help you.
Use means to employ something for a purpose or to put something into action to accomplish a task. When you use a pencil, you're picking it up to write or draw. When you use your brain to solve a math problem, you're applying your thinking skills to find the answer.
The word appears everywhere in daily life. You use a fork to eat, use a calculator to check your arithmetic, and use words to express your ideas. A carpenter uses a hammer and saw. A scientist uses a microscope to examine tiny organisms. What matters is that you're taking something (a tool, a skill, an object, an idea) and making it do what you need it to do.
As a noun, use can also mean the purpose something serves. A screwdriver has one use: driving screws. But many things have multiple uses: a cardboard box might be used for storage, turned into a fort, or recycled into an art project. When something has no use, it means it serves no helpful purpose. When something comes in handy or proves useful, it turns out to be just what you needed.
People also talk about being used when someone takes advantage of them, treating them as a means to an end rather than respecting them as a person. That's quite different from the helpful, practical meaning of putting tools and skills to work.