Supraclavicular brachial plexus blocks provide anaesthesia for the upper limb below the shoulder, excluding the medial upper arm. There are a number of great resources to guide you through learning the block. The addition of ultrasound has greatly improved the safety of this approach compared.
If you need to revise the anatomy of the brachial plexus have a look at this page from Medscape
Medscape -brachial plexus anatomy
NYSORA have a fantastic page detailing the anatomy, ultrasound anatomy and injection technique. They include a useful flow chart to guide you through the process of identifying the brachial plexus.
NYSORA - ultrasound guided brachial plexus block
Sonoguide provide a brief outline of the technique and potential complications. Flash is required to view the video clips
Sonoguide - supraclavicular brachial plexus block
Neuraxiom's page provide the usual high quality illustrations which make understanding the technique and the ultrasound images incredibly simple
Neuraxiom - The Supraclavicular Brachial Plexus Block
Sonosite have produed a number of videos detailing the technique. The '3D - how to' video makes it particularly easy to understand what you will see in your ultrasound image