A Relative to Previous Procedure site is a waypoint defined in relation to the end of the previous procedure.
In the drop-down menu, select True Bearing or Magnetic Bearing to define the bearing of the site's position with respect to true or magnetic north (respectively) or select Relative to Previous Course to define it with respect to the final course of the previous procedure. For example, if you select a bearing of 180 degrees and are using a true or magnetic bearing, then the waypoint will be placed due south of the aircraft's position at the end of the previous procedure; if you are using the Relative to Previous Course bearing, then the waypoint will be placed directly opposite (i.e., behind) the aircraft's heading The direction that the aircraft is pointing. at the end of the previous procedure.
You can enter the Bearing and Range of the site manually or you can click Paste to define them using values stored on the clipboard. In addition, you can calculate values for Bearing and Range by clicking Compute... and entering other values that you know, such as the target latitude and longitude, in the window that appears; click OK to accept the calculated values and return to the site properties window.