What initial step does Prim's algorithm take?

Prim's algorithm begins by choosing any vertex to start constructing the minimum spanning tree (MST). This initial choice doesn't have to be the smallest edge or depend on the weight of any edges; it simply requires a point from which to begin connecting other vertices. By starting at any vertex, Prim's algorithm can then explore and add edges, gradually expanding the tree by always selecting the smallest edge that connects any of the vertices in the tree to a vertex outside of it.

The key aspect of this initial step is that it provides flexibility; any vertex can be the starting point, which allows for various implementations of the algorithm while still producing the same result in terms of the minimum spanning tree. The algorithm then proceeds to grow the tree based on the weights of the edges rather than the starting point.