If you know very little about metal detecting, and want to find out what  is all about, then there is plenty on the Web. Just go to Google (http://www.google.co.uk) and enter metal detecting or metal detecting beginner and you will find more than enough information, so I don't intend  to repeat this information on this site. However, as a basic introduction, I have reproduced below a leaflet, issued by FID, which will get you started.