There is a wonderful online resource available providing maps of electoral areas at http://www.election-maps.co.uk/index.jsp
The key units are
* Parliamentary Constituencies - one MP is elected by each constituency.
* Wards - these are the basic building blocks of each constituency. Wards, ideally, should not be split between constituencies. They are the electoral districts for local elections. ("Electoral Divisions" are the districts for County elections - they made be the same as a ward or bring together a number of wards).
The map in today's picture is Milton Keynes South (effective from the next election). I live in Furzton ward.