Could someone explain this to me, i have no idea what to do

Let's take the movement of the pendulum to the right as positive-y and the movement to the left as negative-y. When the pendulum is at rest, the curve will be at y = 0

The initial position of the pendulum is +12 so we start our curve at y = 12 when x = 0 (because the initial time is when x = 0)

The pendulum swings back to its zero position in 8 seconds, so on the graph this means when y = 0, x = 8

The pendulum swings to the left, and will reach its furthest position at y = -12 and by now the x = 16 (eight seconds from the previous position).

When x = 20, the pendulum is nearly halfway back to its resting position

The graph is shown below