Stand on the shore and watch a ship sailing away. Can you see the lower hull of the ship for the same length of time that you can see the upper decks? No, the curvature of the Earth blocks your view of the lower parts while you can still see the upper ones.
Watch lunar eclipses. When you see the first one, you may think it is just a coincidence that the shadow of the Earth has a round edge. But you will see the same no matter how many eclipses you watch, from anywhere in the world. If the Earth was a flat plate, the shadow would sometimes have a narrower curve, or even be a straight line. But you will never see this, because the earth is in fact round.
On the equator, at noon on the date of the Spring or Autumn Equinox, the rays of the sun will shine straight down a well and illuminate the bottom. At the same time, but further north, the light of the sun will hit the north side of the well instead of shining straight down; south of the equator, the light will hit the southern wall instead. You can hang a plumb line down each well to determine that it is vertical according to gravity, yet the sun shines at a different angle the further from the equator you go. If the earth were flat, this would only be true if the sun were very small and close to us. But if that were true, astronomy would work very differently.

Ref: https://www.quora.com/profile/Ron-Swartzendruber