The Channel Islands are located just off the coast of France mainly in the Bay of St Malo. Formally they are Crown Dependencies, which means in simple terms they are self-governing in all respects except for Defence and Foreign Affairs, which is the responsibility of the United Kingdom.
The Islands fall into two separate Bailiwicks (historic feudal divisions), each of which has its own separate government. Guernsey, Alderney and Sark (comprising the Bailiwick of Guernsey) is effectively a Customs Union with no customs controls between them (despite the fact that Sark levies taxes on alcohol and tobacco at a much reduced rate to the rest of the Bailiwick!)
Bailiwick of Guernsey Smaller than Jersey, and pretty, with a smaller town but less open countryside than Jersey. It also includes the islands of Alderney, Sark, Herm, and many smaller offshore islands.
The Channel Islands have been inhabited for over 5,000 years and have a long and colourful history. During WWII they were occupied and retain many military structures, both from this period and from the time of the Napoleonic Wars.
They count their independence of any ties to France from the year 1204.
Today, the Islands' Head of State is the Queen of United Kingdom who is represented in the Islands by her Lieutenant-Governors. Her role derives from Her status as the successor to the now-defunct Dukedom of Normandy (the Islanders' version of the Loyal Toast, is "The Queen, our Duke". The Islands laws are a mixture of local legislation, customary law (heavily influenced by the English Common Law), Acts of the UK Parliament which have been extended to the Islands and (some) European Union Law in respect of (e.g.) the free movement of people and of goods. The Islands have their own tax systems, currencies (at par with the GBP), banknotes, and individual Parliaments. The relationship with the EU is complex and little understood (they are in the European Union Customs Union but outside the ambit of fiscal and social legislation, for example).