I'm really confused by pivot points and origins. Help?

Practicing blender and trying to learn it better. I started by creating cubes and then turning them into really long rods like pillars and placing the origin either at the bottom center or bottom leftmost edge, to practice snapping them onto a flat plane like a wall, the idea is to get it to sit at the very end of the wall, and snap to the very far edge. What ends up happening though even though I have the origin point in the dead center on the bottommost edge, it snapped to the corner of the cube/pillar and I'm not really sure why. I used all of the combinations of snapping and none of them seem to work very well except maybe perpendicular edge but even then it's kind of janky how it works.

Any tips on how to align them perfectly every time? Assuming we have just a straight flat plane, and a cube or something that you want to align perpendicular