Which model of Sharp microwave do you have?
For the SMC1441CB, after setting the cook time, press the power level button and then the appropriate digits for the percentage of full power to use. For full power, press power level then 1 and then 0. For 50% power, press power level then press 5.
For the SMC0710BB, after setting the cook time, press the Power button until you see the desired power level displayed on the LCD screen. Press Power once to get 100% power. Press Power 6 times to get 50% power.
For the R-659YW, you set the power before setting the cooking time. You press the Power button several times to get to the desired power level. Pressing Power 7 times will have the microwave cook with 40% of its full power level.
Many current Sharp appliance manuals are available on their product page or the Sharp support page. The current Sharp microwaves are listed here: http://www.sharpusa.com/ForHome/HomeAppliances/Microwaves/Models.aspx?facet:configurationfilter=Countertop
. Other appliance manuals are available when you enter the model number in the search bar at http://www.sharpusa.com/Support.aspx
I hope this helps.