Here are some examples of specific language you can include in your will:
To leave a specific percentage, or dollar amount of your estate:
"I give and bequeath ___% (or sum of $___) of my estate to the National Kidney Foundation, (region and address) to be used for its general purposes."
You may also give a particular asset ("my shares of XYZ stock…") or a portion of the residue of your estate after other bequests have been paid ("50% of the rest, residue and remainder of my estate…").