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]])
This is another name for 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.
"taught the people while he sat in the boat." Jesus was in the boat a short distance from the shore and he was speaking to the people who were on the shore.