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KeyboardState provides the capability to read whether a key is down or not. If you need to check if a key was just pressed, so that the user needs to release it then press it again for something to happen, you'll need to track the previous state of the keyboard and update it each frame.
Here's an example of how to do this. Once you've got the previous state of the keyboard, you will have to check if the key in that state is up and the key in the current state is down. This means the user just pressed that key on this frame. I hope that helps!