Each state has 2 senators and terms are 6 years, staggered.
Georgia was due to elect one regular seat (hopefully replacing the horrid David Perdue) and, due to a bizarre fluke, the other seat also needs to be filled, due to it being currently filled by a temporary replacement appointed by the governor last year. Both elections last month were so close that runoffs were required.
Currently, the Senate has 50 Republicans and 48 Democrats. If Democrats can win both seats, the count is 50-50. In the case of a tie, the Vice President has the deciding vote, and that would be Harris. Unless Democrats win not one but both seats, control stays in Republican hands.