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.

Here, I am confused for a long time. Could you please tell me the difference between the two kind 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 am not understand why the book uses defferent 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 useing one symbol for differential, $D$, to take the place of the original symbol, $d$, is enough?