It is in some ways similar to an internet based VPN (Virtual Private Network) in the setup... but very different as well.

MPLS in its root is a signal formatting that allows traffic to be tagged and prioritized. Ultimately, carriers either run MPLS over their IP network cloud or some maintain a separate network cloud for MPLS only. Either way, you connect into the cloud via whatever you need. Could be a T1 or bonded T1s for one location, full or fractional DS3 for others, etc.

Each location comes into the cloud and is notated where it wants to go to. Unlike a point to point T1 setup... you can get any site to any site communication. Similar to internet, you pay for loop and bandwidth amount, so you can take say 10 meg on a DS3.

If you order or receive COS, Class of Service, on the circuit, you can then prioritize traffic. So, for example, all voice over IP would take precedence through the network and override other bandwidth. Video may be second. Network traffic third. General internet usage 4th, etc. You can also dedicate burstable bandwidth amounts from each location for this.

MPLS stands for (Multiprotocol Label Switching).