It's sad that it needs to be said at all, but the Earth is not flat, and humans have known and been able to prove that for a long, long time. At least 2,000 years, in fact.
Greek mathematician Eratosthenes showed it way back in 240 BC, when he used the high tech method of putting sticks in the ground and measuring the angles of their shadows.
Nevertheless, a stubborn group insists that the Earth must be flat for some reason, but there's a campaign now in progress to send one of them up into orbit to see for themselves.