After your W,A,S,D conditions, on the actions side add a force under the Movement>Add A Force. Enter in a force for the needed axis, for the axis not needed Example: W —>Add a force -100 on the Y axis, 0 on the X axis. Etc…
Use a built-in movement behaviour like platformer or top-down movement (and change the keys if you want)
Apply a force to the player object in a particular direction, when a chosen key is pressed
Adjust the X or Y position of the player object, when a chosen key is pressed
The third one is simpler if movement at a constant speed is OK, as your event is just something like:
D key is pressed | Do +4 to Player.X()
to move right or
S key is pressed | Do +4 to Player.Y()
to move down
Forces can give smoother movement, and movement at all sorts of angles, but there can be problems if you want to check an object has reached a particular position as forces can place the object position in between pixels. It is not so suited to tile-based movement for that reason, as you aren’t guaranteed to always align with the tiles.