Special relativity gives every mass in the universe its own clock. I have one, you have one, and so does every planet, but they only keep the same time if they have the same speed. General relativity adds that gravity alters time as well, so it takes a lot of computing to make GPS navigation work because the clocks of satellites tick at a different rates depending on their altitude and speed.
How then does gravity affect time? A virtual time ticks by as processing cycles complete, and more processing takes longer, so it will slow down that time. The earth’s gravity increases the processing load closer to it, which slows down our time. A clock on top of the Empire State building then ticks faster than one at the bottom because the load there is less, while at the bottom, space has more to do, so time passes more slowly there.
Would we then live longer on a planet like Jupiter that has more gravity? To others it might seem so but to us, time would pass as usual. A large planet dilates time relative to earth, but the number of events in our lifetime wouldn’t change, so we wouldn’t notice it.
We feel gravity as a force, see space as an extent, and experience time as life events, so why they relate as relativity says isn’t obvious. In physical terms, they correlate, so space-time changes seem to cause gravity, but in quantum terms, the same activity generates them all. The earth’s distribution causes gravity and alters space and time, so they are all effects not causes.