AdjacencyList

AdjacencyList[g,v] gives a list of vertices adjacent to vertex v.

AdjacencyList[g,patt] gives a list of vertices adjacent to vertices that match the pattern patt.

AdjacencyList[g,patt,d] gives a list of vertices that are at distance at most d.

AdjacencyList[{v->w,…},…] uses rules v->w to specify the graph g.

Examples

Get vertices adjacent to vertex 1 in a graph:

AdjacencyList[Graph[{1 -> 2, 2 -> 3, 1 -> 3}], 1]
(* {2, 3} *)

Please visit the official Wolfram Language Reference for more details.