Junctions, (also referred to as Nodes), represent intersections. A SUMO junction is equivalent to a Vertex in graph theory.
Example of different junctions
In the SUMO-context, edges represent roads or streets. Note that edges are unidirectional. It's equivalent to a edge in a graph theory.
Example of edge. Note that the box "select edge" is checked
Each SUMO edge is composed of a set of lanes (At least one).
Example of lane. Note that the box "select edge" is unchecked
Connections describe how incoming and outgoing edges of junctions are connected (for example to prohibit left-turns at some junctions.
Example of connection between a source lane and a target lane
A traffic light program defines the phases of a traffic light.
Example of Traffic light