This phrase is used here to mark the beginning of a new part of the story. If your language has a way for doing this, you could consider using it here. (See: [[rc://en/ta/man/translate/writing-newevent]])
These words refer to the Sea of Galilee. Galilee was on the west side of the lake, and the land of Gennesaret was on the east side, so it was called by both names. Some English versions translate this as the proper name of the body of water, "the Lake of Gennesaret."