Tracks are usable in both Physics and Discrete Event Mode.
In Discrete Event Mode the tracks are the base components for doing discrete simulation.
The idea is to route loads around in a network for routes.
By connecting routes (snapping tracks together) the route graph is calculated based on the nodes (action points) in the network.
Tracks, by default, run from the red point to the blue point, so when attaching additional tracks, opposite coloured points must be snapped together to ensure the model flows correctly.
To join the tracks together, move them together so the the blue and red connection points merge, while holding down CTRL, so the two components will snap together.
To merge tracks drag one track over the other until both highlight, then hold the CTRL key to snap them together.