Help with ATR-72 (and generally) regarding LNAV and autopilot

I am relatively new to msfs (only played the game for a handful of hours when it was released) and decided (for better or for worse) than the ATR-72 would be the first aircraft I fly.
While I have been able to solve most of the steep learning curves of preparing and flying the aircraft through trial and error, one major issues persist: I am unable to find out how to enable LNAV on the ATR (or in other words, get the aircraft’s autopilot to follow the waypoints on my flight plan). Whenever I engage autopilot, the plane keeps climbing at a steady rate (I assume to cruise), but I still have control over the horizontal movements of the aircraft. For reference, I am creating a simple flight plan from the pre-flight menu with IFR high altitude airways+SID,STAR and approach. I am aware that there is a computer provided by the developers in the ATR for flight planning etc. but so far I haven’t figured how to log onto it and regardless I don’t think its necessary for flight planning,
I’m not even sure how to program it to climb and hold a certain altitude, all I’m doing at the moment is placing it in autopilot (which puts it in a steady climb), then altitude hold when I reach cruise. I am still also yet to figure out how to fully program VNAV (does the FPL do that for me with the STAR wpt altitudes?

Therefore, a general guide on how to file detailed FPLs, along with how to use the autopilot/LNAV on aircraft (ATR specific perhaps) would be greatly appreciated. If anyone has any video suggestions then it’d also be welcome.

A real ATR pilot named Magnar has a series of detailed tutorials on flying the ATR in MSFS in Toutube. His channel is Fly with Magnar. Im no expert but I have the ATR pretty well figured out. If FP is properly set in your FMC what I do is set the initial flight level on that knob, set the takeoff runway heading with that knob, hit HDG button, the NAV button and the IAS button. PFD should show Heading Sel in green at top left with LNAV below it in blue, then LO in the next window. IAS next and FD at too right. Take off and at permissible height hit AP. AP and YD shoiuld both light up

Oh. To set flight plan using the electric flight bag you log in first using your Simbrief Id No. I dont think VNAV works yet so to climb or descend to new FL I use VS and nose up or nose down and watch air speed. The ND will show you where you will get to new FL at a particular VS

Thanks for your help, and do you ensure FPL is in the FMC