The rows (I guess you refer a row to a set of 4 DH-parameters) represent, roughly speaking, every link. So it's
When deriving DH parameters, the base frame usually situates at the robot base, where it is mounted on to floor. This DH convention is a convention that tells you how you put reference frames on a robot. How many frames you need (apart from the base frame) depends on how many joints there are. This corresponds to how many links you have.
So for a 2 degrees-of-freedom (DOF) robot as shown, you would have 3 sets of DH parameters. Each set, consisting of link length, link twist, link offset, and joint angle, describes each link.