I have the 737 PMDG and am starting to get my head round the FMC. I programme in everything i need to like waypoints etc. When i take off, do i use the autopilot Lnav for it to follow the course planned by the FMC and do i still need to use the speed button and auto throttle when following the course.
You should take the time to read the manual and do a couple of tutorials. In general I could tell you that you should program the FMC properly (i.e. do the initialization page, the route, departures/arrivals if needed, weights, speeds, vnav) and then all you need to do is click VNAV and LNAV. The plane will take you where you want to go.