How to read the block diagram for the 2nd order integrator feedback system?

This is a prework for a lab, I haven't seen things in the picture before and have no idea on how to transfer this to an equation.

$$\frac{dy}{dt} = x_1$$ $$\frac{dx_1}{dt} = x_2$$
$$x_2 = x(t) - a_0 y(t) - a_1 x_1$$