I have been detecting for the last couple of years. It is a great hobby if you love history and the outdoors. If you go into it looking for treasure you will probably get frustrated and give up.
The law in England is quite reasonable. You must have the landowner's permission. Anything you find belongs to the landowner although if it is to be sold there is a legal precedent of a 50:50 split.
To avoid disturbing archaeology it is good practice not to dig deeper than the plough. Everything in that level is out of historical context and you are saving it from further damage. In England you should report historical finds to the "Portable Antiquities Scheme". This helps build up a picture of historical clues that is open to all researchers.
Silver of gold objects older than 300 years must be reported to the coroner within 14 days. They belong to the nation but you will eventually get paid a very conservative estimate of their value. Similarly 2 or more silver coins more than 300 years old that went into the ground together - or 10 copper ones - must be reported.
I ma lucky to live in a rural estate that has been inhabited for many centuries. I have found around a dozen old silver coins and loads of medieval and post-medieval artifacts.
Here is couple..
King John cut half Penny dated approx 1200 ---------------- Medieval Dagger Pommel
Henry VI Groat dated approx 1422 -------------------- Queen Victoria Gold Sovereign dated 1900
Possibly the most stunning hammered coin ever. It's a Charles I threepence from 1644 minted in York a few years before they cut his head off.