How do pilots calculate their rate of descent so that they’re at ground level when the reach the runway?
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What I am about to describe is true for most modern airliners.
From cruise to the beginning of the approach we use something called VNAV which is short for Vertical Navigation. The flight management system calculates a descent with ideally idle thrust. We input the wind and the FMS more or less does the rest. Quite often ATC will screw up our plan though by not letting us descend when we want to. In that case we can use our judgement or a few other predictive tools we have. Based on our current ground speed and descent rate most modern aircraft will be able to predict (and display on the map) where we will reach our target altitude.
Now, once we are on the approach (usually 10-15 miles from the runway and around 3000 feet above the ground) we will typically use either an electronic glide slope from a ground based navigation aid installed next to the runway, or we can use a GPS-calculated glide path from the FMS. Not all planes are capable of this but most modern airliners are.
Additionally, many runways have a visual glide slope aid called either PAPIs or VASIs. As others have mentioned these are four red and white lights that tell the pilot if they are too high or too low. Four white lights means we are too high. Two white and two red means we are on the right path. Four red means we are too low.
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