Steve_H
You wear a mask to prevent you (the wearer) spreading droplets to others.
The faceshield it to protect the wearer from droplets fired out by others.
That's the really simple explanation but there is more to it, for example stopping you touching your face as much.
Wearing either, or both, doesn't guarantee you protection from Covid, but it does stack the odds more in your favour.
The safest thing is distance, a 2m stick with a spike on the end helps, although though I find been an antisocial sod and avoiding any contact with humanity works best ๐