Assuming your tap has a threaded spout:
One of these on the tap and one on the pressure washer:
http://www.amazon.co.uk/Hozelock-4-inch-Metal-Threaded-Connector/dp/B0034G5NSG
One of these on the tap end of the hose: http://www.amazon.co.uk/Hozelock-2050-Hose-End-Connector/dp/B001OXFHVY
One of these on the other end of the hose:
http://www.amazon.co.uk/Hozelock-Ltd-2055-0000-Connector/dp/B001OXDE0K/
And a hose, of course.
Pop down to a garden centre!!
XXX, April 2016