The Privy Council goes back to the earliest days of the Monarchy, when it comprised those appointed by the King or Queen to advise on matters of state. As the constitution developed into today's constitutional monarchy, under which The Sovereign acts on the advice of Ministers, so the Privy Council adapted. Its day to day business is transacted by those of Her Majesty's Ministers who are Privy Counsellors, that is all Cabinet Ministers and a number of junior Ministers. Membership of the Privy Council brings with it the right to be called "Right Honourable". A list of Members of the Privy Council.
The Privy Council still meets regularly, on average once a month, but, as with the Cabinet, most of its business is transacted in discussion and correspondence between its Ministerial members and the Government Departments that advise them. The Privy Council Office (which is itself a Government Department) provides a secretariat for these discussions, as the Cabinet Office does in relation to the business of Cabinet and Cabinet Committees. Councils are held by The Queen and are attended by Ministers and the Clerk of the Council. At each meeting the Council will obtain Her Majesty's formal approval to a number of Orders which have already been discussed and approved by Ministers, much as Acts of Parliament become law through the giving of the Royal Assent after having been debated in Parliament.
Meetings are reported in the Court Circular, along with the names of Ministers attending (usually four in number). The Orders made at each Council are in the public domain, and each bears the date and place of the Council at which it was made. There is therefore nothing at all "secret" about Privy Council meetings. The myth that the Privy Council is a secretive body springs from the wording of the Privy Council Oath, which, in its current form, dates back to Tudor times. It requires those taking it to "keep secret all matters...treated of in Council". The Oath (or solemn affirmation for those who cannot take an Oath) is still administered, and is still binding; but it is only in very special circumstances nowadays that matters will come to a Privy Counsellor on "Privy Council terms". These will mostly concern matters of the national interest where it is important for senior members of Opposition parties to have access to Government information.
Commentary on the Council, its powers and functions coming from a Marxist is at What's It For? - http://www.lrb.co.uk/v37/n20/martin-loughlin/whats-it-for. He manages not to notice the duty of loyalty to the Crown.
A list of Privy Councillors is at Counsellors.
You do swear by Almighty God to be a true and faithful Servant unto The Queen’s Majesty as one of Her Majesty’s Privy Council. You will not know or understand of any manner of thing to be attempted, done or spoken against Her Majesty’s Person, Honour, Crown or Dignity Royal, but you will lett and withstand the same to the uttermost of your power, and either cause it to be revealed to Her Majesty Herself, or to such of Her Privy Council as shall advertise Her Majesty of the same. You will in all things to be moved, treated and debated in Council, faithfully and truly declare your Mind and Opinion, according to your Heart and Conscience; and will keep secret all matters committed and revealed unto you, or that shall be treated of secretly in Council. And if any of the said Treaties or Counsels shall touch any of the Counsellors you will not reveal it unto him but will keep the same until such time as, by the consent of Her Majesty or of the Council, Publication shall be made thereof. You will to your uttermost bear Faith and Allegiance to the Queen’s Majesty; and will assist and defend all civil and temporal Jurisdictions, Pre-eminences, and Authorities, granted to Her Majesty and annexed to the Crown by Acts of Parliament, or otherwise, against all Foreign Princes, Persons, Prelates, States, or Potentates. And generally in all things you will do as a faithful and true Servant ought to do to Her Majesty