We wish to show that for a path connected space X, the zeroth singular homology group is just Z.
The intuition is that the zeroth homology group is given by consider C[1]∂1C[0],
C[0]∂00, and then taking H[0]≡ker(∂0)/im(∂1)=C[0]/im(∂1).
Recall that C[0] is the abelian group generated by the direct sum of generators
{Δ0→X}, where Δ0 is the 0-simplex, that is,
a single point. So C[0] is an abelian group generated by all points in X. Now, C[1] contains all paths
between all points p,q∈X. Thus the boundary of C[1] will be of the form q−p. Quotienting by C[1]identifies all points with each other in C[0]. That is, we get H[0]≡⟨x∈X∣y=z∀y,z∈X⟩,
which is isomorphic to Z. Thus, the zeroth singular homology group is Z.