Does the book of Genesis or some other book of the Bible say the Earth is flat?
No, the Bible does not say that the Earth is flat. There are some common idioms the Bible uses that if taken literally might give the impression that it's claiming the Earth to be flat, but idioms are not meant to be taken literally. After all, if you tell me something outrageous and I say, "You're pulling my leg!", am I accusing you of a physical assault or accusing you of telling a fib or a joke?
One such example is the expression "the four corner of the Earth." This idiom is used only when expressing how far something is to travel (Rev. 20:8) or to emphasize the vastness of something (Is. 11:12). This phrase is also used simply as an expression of north, south, east, and west (Rev. 7:1). Even in biblical times, people usually traveled with a flat map that had four corners. If you were to travel to the places designated by the four corners of the map, that would indicate you are traveling "all over" the map, but it is still not an attempt to state a fact about the shape of the Earth.
Another common idiomatic biblical expression is "the ends of the earth." But once again, it is an expression of great distance and not an attempt at a factual statement.
The reality is that most ancient people knew the Earth was a sphere; the only question was how large of a sphere. The idea that the Bible teaches the Earth is flat gained traction only in the Fundamentalist movement in the nineteenth century.