Create a macro(?) to hold 2 keys at the same time?

Hi everyone...i need some help with the macro funcionality.

I need to create a macro where when activated, the "S" and "D" keys should be hold at the same until i deactivate it, making my character in the game walk backwards and to the right, so he will be walking in circles...

Any idea on how i could do that?

I tried some ideas from other threads but i couldnt make it work the way i wanted...

Thanks!