[MisterPC]

Robert Sedgewick's course [1] and associated book/booksite [2] have a good overview of Union-Find problem and various algorithms to solve it.

[1] https://www.coursera.org/learn/algorithms-part1

[2] http://algs4.cs.princeton.edu/15uf/

[Apocryphon]

Indeed, Union-Find is the first subject the course covers, because it uses it as an example of an elementary algorithm.