Traditionally calls are routed to the longest waiting agent. With skills based routing, the call center routes all types of interactions, including calls, to the agents who are best equipped to handle the interactions.
In Interaction Architect, formerly named Call Plan Architect, you must create an Automatic Call Distributor (ACD) applet and run the applet in skills based mode. In skills based mode, the ACD applet becomes a Universal Contact Distributor (UCD) applet and routes an interaction to the agent who has the required skills for dealing with the interaction.
For information on using skills based routing, see Setting up skills based routing.