The IFD FMS is a convenient device which makes the planning and execution of flight plans simple.
Under the FMS tab on the IFD, look at the FPL tab. You should be seeing a black screen with a thin blue line known as the "Input Cursor" Touching this cursor will bring down a drop down menu. Origin and Waypoint are presented. Selecting one will be the "anchor" for the flight plan to build upon.
A sample flight plan is listed below:
(Melbourne to Lakeland shooting the RNAV Runway 5 approach)
KLAL--(here we want to touch the Approach tab in the KLAL box and select the RNAV Runway 5 approach)
(RNAV 5 via SANOY as the IAF--Initial Approach Fix)
Activate flight plan using the LSK (Line Select Key) or touchscreen.