This piece will have your sprocket mount to it. You can put it either direction but make sure the key (the 2 inch long small metal piece that goes into the axle and a slot in the mount) is all the way through the keyhole.
Note: you may also have this sprocket mount outside the frame next to the wheel hub. My motor is facing toward the driver, some (maybe most) motors will face away from the driver.
Now you want to be thinking of your chain alignment and where your motor shaft will be.