The Open University makes some of its study units freely available online. This one in particular provides an introduction to key concepts underpinning the study of international law.
It looks at international legal personality, explores the status of the State, examines the principle of sovereignty and summarizes the principles of jurisdiction. The focus is on areas of special relevance to contemporary events.
You will find the above international law unit here.
Other units that might be of interest: Corporate responsibility for industrial incidents; An introduction to law in contemporary Scotland; Europe and the law.
You might also like this post on Free learning resource on law.