I began to appreciate some ideas of algebraic topology originally through differential topology, in the form of my own discovery of the meaning of the advanced calculus theorem called greens theorem. The problem was to comp0ute the fundamental group of the punctured plane, R^2 - (0,0). I.e. we want to show that the unit circle cannot be moved continuously, within the punctured plane, so as to no longer wrap around the origin. We weaken our request to try to show rather that it cannot be so moved differentiably. Take enough time, as much as you need, to realize that moving the unit circle off the origin, since one can then shrink it to a point, means finding a differentiable map from the unit disc to the punctured plane, so that the boundary maps to the unit circle, and the rest of the disc maps into the punctured plane.
So we want to show that no differentiable map of the unit disc to the plane can map the boundary identically to the unit circle, but the rest of the disc misses the oprigin. This follows from the greens theorem. I.e. that theorem says you can compute a certain integral either around the boundary of the disc, or over the disc itself. The second ingredient is the "angle form" dtheta, whose integral is non zero over the unit ciurcle, but whose curl is zero, hence the integral of its curl is zero over the disc. If the map we described were to exist, the greens theorem would then say that zero equals a non zero number, hence impossible.
geometrically one can define the conceopt of "winding number", and use green to prove that winding number does not change under a differntiable motion of the curve. Then one computes that the winding number of the unit circle is one, while that of a circle moved of the origin is zero.
this gets generalized to the concept of fundamental group, or homology of the punctured plane, whihc turns out to be a group whihc is generated by that angle form. I.e. if you understahd the angle form you have understood the fundamental group of the punctured plane as well as the first homology group.
ramping up, there is a solid angle form that generates the second homology group of the punctured 3 space, and let's you prove there are no non zero vector fields on the 2 sphere.
I had taken courses in algebraic topology and understood nothing, and then while teaching calculus i asked muyself what good was greens theorem? the answer i dioscovered unlocked the ideas of differential and algebraic topology for me. probably fulton's book and its approach, is closest to my own path.