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). To inspect and edit lane attributes, either SHIFT+click on a lane or toggle the corresponding menu bar button ton control whether inspect clicks should target edges (default) or lanes (shortcut ALT+5).
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