An excellent summary is available on the United Grand Lodge of England website.
Freemasons trace their origins to the ancient fraternity of stonemasons. The degrees of freemasonry retain the three grades of medieval craft guilds, those of Entered Apprentice, Fellowcraft, and Master Mason. As we are not practising stonemasons, we are referred to as Freemasons, ‘Free’ as in free from working with stone. There are additional orders which a mason can join such as Holy Royal Arch & Knights Templar once he is a member of a lodge.
The basic unit of Freemasonry is the Lodge. The Lodges are usually supervised and governed at the regional level (Ipsley Lodge is governed by the Provincial Grand Lodge of Warwickshire) by a Grand Lodge, in our case the United Grand Lodge of England.
A typical lodge meeting will have several procedural and administrative points (minutes, reports from officers etc) but the main activity will usually be a ritual ceremony. There are three main ceremonies, Initiation (Entered Apprentice) Passing (Fellowcraft) and Raising (Master Mason). Once a year there will be the Installation of the New Worshipful Master
Freemasonry does not discriminate on grounds of colour, race, religion, political leaning or background.