Here's a video for you, Barbara:
You should be able to unscrew the cap where the water comes out and the screen is inside. Be careful to close off your drain or you will lose the screen when you pop it out of place. Rinse it and then put it back. If you use a wrench to loosen it be sure to put a cloth on first so as not to scratch it.
If you can unscrew take the aerator off and let it soak in in a small container or in a large bottle cap with vinegar for 15 minutes or so, rinse and reinstall. Sometimes the aerator is so limed up it is next to impossible to be removed without damaging it, then I tape a small container filled with vinegar to the spout with masking tape to dissolve the lime around the aerator.