Answer:
fasten things, hold/pull things, amplify force
Step-by-step explanation:
A screw is a type of simple machine.
It can be used to fasten 2 or more things together (ex planks of wood). It can also be used to pull something by screwing into the material and staying there (ex corkscrew for opening wine bottles). It can also be used to magnify force. You can tighten a wingnut by hand and get a significant amount of vertical holding power.