Articles about Spanning-Tree Protocol and Root Guard, Loop Guard etc

• Spanning-tree Loop Troubleshooting and SafeGuards
• Configuring Root Guard & Loop Guard
• BPDU Guard, BPDU Filter, Root Guard, Loop Guard & UDLD
• What Is the Difference Between STP BPDU Guard and STP Root Guard?

Of course there are more technical and in depth articles at sites such as Cisco.com (here, here, here, here etc.) and others. Google is your friend :-)