"Rail Sweep" picks up your profile from wherever it may be, and extrudes it along the designated preexisting path. It is sometimes difficult to control the orientation of the cross section of the finished Sweep.
"Sweep" starts the extrusion from the current location of the profile, extruding it along a path that is parallel to the designated preexisting one. Recommended practice in most cases is for the user manually to place the profile on the end of the path, with its plane normal to the path, before sweeping.
"Revolve" extrudes the profile along a circular path, starting with the current position of the profile. Radius of the path is defined by the user in accordance with the instructions that appear at the lower left of the screen when using the tool.