I am a beginner to study QFT and confused about path integral for boson or fermion.

I have read about the path integral for single particle, and finished some problems. But I cannot understand the next chapter which is about path integral for boson and fermion. 

What is the difference between the two kinds of path integrals? What is the point of path integral for boson and fermion?

I find that there are big differences in forms between single particle, boson and fermion. I do not understand why the book uses different forms to discuss them. Even the path integral for the spin system has a new form to discuss.

In my opinion, I think the biggest difference between single particle and boson (fermion) is statistics, but how to consider about the statistical properties in path integral? Just using one symbol for differential, $D$, to take the place of the original symbol, $d$, is enough?