Velocity x vs Time t

xo(m)   vo (m/s)   ao(m/s2)   da/dt(m/s3)
A straight horizontal line in a graph means that your dependant variable does not change. In this case, the variable is the velocity. The straight horizontal line means that the velocity is constant.
Note that the curve does not provide information about the initial position of the puck. For this reason, you had to leave the xo box blank.
However, to simulate the motion, we had to arbitrarily select an initial position. In this case, the initial position on the simulation was set to zero.