Empty the cabinet
Remove anything you are storing underneath the sink.
Place bucket underneath the trap.
Spread your towel on the floor of the cabinet in case of any water drips. Place the bucket or basin underneath the trap.
Loosen the coupling
Loosen the coupling where it attaches to the downspout. If you have a metal pipe you will need to use your wrench to loosen the nut.
Disengage the pipe
When the back nut is loosened the pipe can be easily disengaged.
Reach into the trap and clear out whatever is causing the clog.
Re-attach the pipe
After you are done screw the trap back into place. Make sure the nuts are nice and tight.