To deliver the club correctly on the downswing you must first learn the three arcs of the backswing so that you get your club in the correct position at the top
Make sure to swing your arms back in the backswing, not away from or in to your body, the arc of the swing and coil of your body will take care of the rest
Slicing is caused by an open clubface, fix this by turning your top hand clockwise and practice swinging with a closed clubface