Distance is a measure of how far an object travels in total — it is the total length of the path taken, and it is a scalar quantity, so only the magnitude matters and the direction travelled in is irrelevant. For example, if athletes run a $300\,\mathrm{m}$ race on a $400\,\mathrm{m}$ circular track, the distance they have travelled is simply $300\,\mathrm{m}$, the length of track they covered.

Displacement is a measure of how far an object is from its starting position, together with the direction from the start to that position — in other words, it is the change in position. Because it carries both a size and a direction, displacement is a vector quantity. In the same $300\,\mathrm{m}$-race example, if the athletes end up $100\,\mathrm{m}$ from where they started, their displacement is $100\,\mathrm{m}$ in that direction, even though the distance run was $300\,\mathrm{m}$. If the athletes instead completed the full $400\,\mathrm{m}$ lap and returned to their starting point, their displacement would be zero, since they are back where they started — while the distance travelled would still be $400\,\mathrm{m}$.

This distinction — path length versus net change in position — is why distance and displacement can differ for the same journey. A student travelling to school covers a distance equal to the total length of every road, twist, and turn they walk along, but their displacement is the single straight-line vector from home to school, regardless of any obstacles (buildings, lakes, roads) that force them to take a longer path. Distance is a scalar because it only describes how far has been travelled overall, with no reference to direction; displacement is a vector because it describes both how far an object is from its start point and in what direction.