This product is priced per meter so quantity = Meters
An underground cable will normally be laid in a trench, and then the trench back filled to cover it.
The cable needs to be buried deep enough that it is unlikely to be disturbed accidentally in future. There are no hard and fast rules here since circumstances will dictate an appropriate depth. In areas unlikely to be dug over or disturbed such as under a path or a lawn, then shallower burial is acceptable - possibly a spade's blade depth or around 12". For a cable passing under a flower bed, where one could expect the area to be dug over, A typical minimum depth would increase to at least two spade's depth.