Dijkstra’s algorithm is one of those things that are really hard to grasp until you just tinker with them. It’s hard to explain it rather than simply showing.
This post was generously made by a user who wanted to show off not only Dijkstra, but other algorithms for pathfinding like A*. Their game where it is shown is still available. I highly recommend opening the game in studio and tinkering with the code.
This article on Wikipedia has a pseudocode section that does a good job of explaining the basic process of pathfinding through Dijkstra.