They are actually pretty simple. Essentially you generate the Dijkstra values for an undirected graph (this can be a grid, navmesh, etc), then you create directed edges pointing from high values to low values. So a grid space of value 8 will point to its neighbors with values less than 8, etc.
All an agent has to do is query their current spot in the graph and it will return a vector that leads them to the next lowest cost. This is useful if you have lots of agents going to the same location.
The description of this video has a lot of good resources. I made it when I was a much much worse programmer though so I wouldn't bother actually watching the video lol.
