This presentation gives an overview of transportation lanes in SAP TM and SAP TPVS (the functionality is very similar in those products).
It talks about the concept of the transportation lanes, the levels at which data exists, and the granularity of transportation lanes along with guidelines on deciding the granularity.
Also, it goes into different carrier selection strategies and how priority and cost interact.
This presentation does not go into the priorities for broadcast tendering (which is functionality in SAP TM 8.0 and onwards). That will come in update version 3.0.