Character controller with key click to move forward

I want to create 3D character controller where when the 'W' key is pressed once, the player begins to walk continuously until 'S' key is pressed to stop the player. When walking, if 'W' key is pressed again, the player starts to run, until 'S' key is pressed to slow down to walk and then pressed again to stop. I also want to turn the player with 'A' and 'D' keys while walking or running forward.

I'm new at coding so I'd appreciate all the help!