There is definitely a lot of ways to calculate and plan your descent and I have been playing for over a year and I just found the method that I find the most efficient for me and you just need some simple calculations

What you will need:

Your current altitude (MSL)

The elevation at your destination

Your groundspeed

Calculations:

FOR YOUR TOD (top of descent)

Take your altitude (ex: 33000ft)

Subtract your altitude by your destination airport elevation (ex: 33000 - 1269 = 31731)

Subtract this number by 3000 (ex: 31731 - 3000 = 28731)

Divide this number by 100 (ex: 28731 / 100 = about 287)

Divide this number by 3 (ex: 287 / 3 = about 96

So your TOD will be 96nm from the airport

FOR YOUR VS (vertical speed)

Take your groundspeed and multiply it by -5 (ex: 427 x -5 = -2135)

A quick and easy way to calculate the descent. I used these calculations, only I did not know what speed has to be used from the calculated nm and start with the descent.
My other question is, if I go to an altitude of 30,000ft, and I have to start descending at a vertical speed of -1,800, suppose, in my AP, what height should I configure? (3,500 for example)