In Scratch, all the code blocks you can use are on the left side of the screen. They're divided up into different color categories. We want the cat to move when a key is pressed on the keyboard, so that means we want to start with an Event block. Event blocks wait for something to happen, then trigger other code to start running.
Click on the yellow Events circle on the left side of the screen, and drag the block called "when space key pressed" into the blank middle area of the screen.
All the blue blocks in Scratch move sprites around the screen. The "move 10 steps" block moves the sprite 10 steps in the direction it's facing right now.
Click on the blue Motion circle at the left side of the screen, and drag in a "move 10 steps" block. Connect the block to the "when space key pressed" by moving it directly under the Event block until the seem to snap together.
On the yellow "key pressed" event block, click the box with "space" inside. It will pop up a dropdown with a bunch of different keys you can choose. Since we want the cat to move when we press the right arrow key, change "space" to "right arrow".
On the top right of the screen, click the Green Arrow button. This button starts the Scratch program. Then, you can test out your code by pressing the right arrow key on your keyboard. If everything works well, the cat should move right!