A hole can be created in Solidworks in an existing body with the Hole Wizard by doing the following.
Select the type of hole and specify diameter, depth, and other parameters. Select the position tab. Select the face that the holes will propagate from.
Then click to create a center point for the hole. More than one points can be selected and dimensioned to create multiple holes, or a Linear Pattern or Circular Pattern can be used to the same effect.