If you have the type of strut that has a removable plate over it the strut cartridge it can be replaced from the top of the car without having to raise it up and having to remove the entire strut assembly with the coil spring.
The tool is a long tube that goes over the strut rod and has notches on the end that fits the top of the strut and allows you to unscrew the cartridge and replace it.
A 1/2 breaker bar is used to turn the tool.
Your best bet is a parts house to buy the tool or check to see if a tool rental place has one available.

