Handicap Calculation for Steve Tucker for Week 21

Week of Rounds Used:		15	14	13	10	9		Total		Average		90%		Rounded to:
Gross Score:		59	64	53	51	63		290		58.00
Hdcp Score (over Par):		21	24	16	16	23		100		20.00		18.00		18

What does this mean? How are handicaps calculated?