A magnetic field is the region around a magnet or a current-carrying wire where a magnetic force is exerted on a magnetic object. Such a region can be detected using either iron filings or a compass.
Ends of magnetic objects have poles
go from north to south pole
the magnetic field B describes in what direction a small test compass would point if placed at a certain point in the field
magnetic field strength is measured in Teslas and is a vector quantity
in the earth, the north pole is actually magnetic south
magnetic quality of the earth is due to currents of the molten rock, powered by the heat in the core = permanent magnet
(it’s not actually permanent as it inverts every few million years)