What do I need to know about metal detecting?

I am very interested in metal detecting, I don't own one yet but my boyfriends father has one he is giving me. So I'm just wondering if there is anyone on this site who can help me with some questions I have?

*Do I need a permit?
*Are there any laws I need to follow?...I live in Australia.
*How do I know what (and if i need to use) the discrim level to use?

Plus I have many more questions, thanks to anyone who can help me :)