Her Majesty's Most Honourable Privy Council is a group of advisors to the British Monarch. A lot of its most important work is done by two committees,
 The Cabinet. All cabinet ministers are made Privy Councillors (or Privy Counsellors), as are other important politicians, such as the leaders of the big political parties.
 Judicial Committee of the Privy Council. The most senior judges in England and Wales sit on this committee

Some laws need to be made by the "Queen-in-Council", that is at a meeting of the Queen and the Privy Council. Some jobs are filled by the Queen in Council too. For example, when the Queen appoints a new Bishop or Lord Lieutenant she announces her choice at a meeting of the Privy Council.

Meetings of the Privy Council 
Once someone is made a member of the Privy Council they are a member for life, but only members of the government are asked to meetings, except for special occasions such as when a new monarch takes the "Accession Oath", a promise to do their best, at a meeting when the Privy Council called the Accession Council 

In the past some kings and queens were bored by long meetings of the Privy Council, so they made everyone stand instead of sitting comfortably. The tradition carries on today.

Privy Council Terms 
Sometimes the Prime Minister shares information with other politicians on Privy Council Terms. This means that the information must stay secret.

Judicial Committee of the Privy Council 
The Law Lords, and retired Law Lords, also form the Judicial Committee of the Privy Council. It is the final court of appeal from British colonies an dependent territories, and some commonwealth realms. These countries call it an appeal to The Queen in Council.

The Commonwealth Realms 
 Antigua and Barbuda
 Bahamas
 Barbados
 Belize
 Cook Islands and Niue (Associated States of New Zealand)
 Grenada
 Jamaica
 St. Christopher and Nevis
 Saint Lucia
 Saint Vincent and the Grenadines
 Tuvalu

The Overseas dependent Territories 
 The Sovereign Base Areas of Akrotiri and Dhekelia (in Cyprus)
 Anguilla
 Bermuda
 British Virgin Islands
 Cayman Islands
 Falkland Islands
 Gibraltar
 Montserrat
 The Pitcairn Islands
 Saint Helena and dependencies (Ascension Island and Tristan da Cunha)
 Turks and Caicos Islands

Republics in the Commonwealth 
Four republics in the commonwealth also use the Judicial Committee of the Privy Council as a court of appeal.
 Republic of Trinidad and Tobago
 Commonwealth of Dominica
 Kiribati
 Mauritius

Brunei 
From the Court of Appeal of Brunei the only appeal is to the Sultan of Brunei. The Queen and the Sultan have agreed that the cases are heard by the Judicial Committee of the Privy Council who then advise the Sultan, directly.

Domestic Jurisdiction 
The committee hears Appeals to Her Majesty in Council:
 from Jersey, Guernsey and the Isle of Man;
 from the Disciplinary Committee of the Royal College of Veterinary Surgeons;
 against some plans of the Church Commissioners.
 about "devolution issues", (the powers of the Scottish Parliament, or the Northern Ireland or Welsh Assemblies) if

 A Law Officer refers a Bill, directly to the committee.

 there is an appeal from certain superior courts of England and Wales, Scotland and Northern Ireland.

 Devolution issues can be referred to the Judicial Committee by -

 certain appellate courts, including the House of Lords, and

 any court or tribunal, if required to do so by the appropriate Law Officer.

 A Law Officer refers "devolution issues" that are not about current bills.

Very rarely the Committee hears:
 Appeals from the Church of England's Court of Arches  of Canterbury and the Chancery Court of York.
 Appeals from Prize Courts,which hear the value of ships and their cargo.
 Disputes under the House of Commons Disqualification Act, about whether someone is allowed to be a Member of Parliament
 Appeals from the Court of Admiralty of the Cinque Ports.

The committee must also report to the Queen about anything she ask. For example, investigating which members of the House of Lords supported the enemy in World War I.

References 

Politics of the United Kingdom