thermodynamics - Question about Ginzburg-Landau Theory

I was reading CH3 of Reichl's "A Modern Course in Statistical Physics" on Ginzburg-Landau theory and don't really understand a couple of points he makes. He writes:

I don't understand why the first order term in $\eta$ would imply a nonzero value of the order parameter above the transition point, and I don't really get the motivation for the $-f \eta$ term either. If you had the $\eta \ \alpha_1(Y,T)$ term then $\frac{\partial \phi}{\partial \eta} = \alpha_1 + \eta \alpha_2 + ... - f=0$ then putting $\eta=0$ doesn't work so I guess that kind of makes sense, but then you have this $-f$ which would seem to mess things up anyway.