Unstable manifold of height function on torus

Question

I am currently reading Morse Theory. From the following picture I have to calculate the unstable manifolds of different critical points. Here our Morse function $f:T^2\to \Bbb R$ is the standard height function from $z$-plane. What I know that, $p,q,r,s$ are the only critical points having indices $0,1,1,2$ respectively, of $f$. But, I can not understand the way of finding unstable manifolds. I can do this if I know how does the flow lines look like. Any help with intuitive or rigorous explanations will be appreciated.