Summarised here:
http://en.wikipedia.org/wiki/British...f_World_War_II
There are a number of books on Operation Sealion.
Two I have read, both fairly concise:
- Cox, Richard (1977). Operation Sea Lion. Presidio Press. ISBN 0-89141-015-5
- Macksey, Kenneth (1980). Invasion: The German Invasion of England, July 1940. MacMillan Publishing Co. ISBN 0-02-578030-1