This site is being deprecated.
Please see the official X‑Plane Support page for help.
Have you followed the tutorial that came with X-Plane 11? It’s the file “X-Plane FMS Manual.pdf” located in the “X-Plane 11\Instructions” folder. It contains a step-by-step example route for LNAV and VNAV; simple, but a place to start for the Laminar’s FMC.
That said, the default FMC in XP11 is a simplified version of the actual thing. I found the operation associated with the autopilot to be hit-and-miss, sometimes. For a more realistic and reliable sim experience, you need a dedicated FMC built for the specific aircraft—often only found in more expensive payware airliner. The freeware Zibo B738 mod does have a much improved implementation.
This site is no longer being actively maintained.