sorry for not writing such long time, I was enjoying holidays for whole week. Anyway I am coming back with post about tidal force.
Tidal force is effect of gravitational force and it can be seen as for example tide.
So you have Moon which is attracting everything, even water in our oceans. Water closest to Moon is attracted with greatest force while water far away with least. As you can see on the picture there is Moon (Satellite) on the right this grants us two high tides per day.
So as is Moon orbiting it changes the place where low and high tides are.
This effect creates amazing things: rings! Planetary rings can be made by some satellite which moved too close to its planet and tidal forces were so strong that it ripped it apart, so there is higher probability that larger planet will have ring.
Tidal force also can be “seen” in effect called spaghettification which is made by black holes or other massive objects.