WHAT'S A BAR MAGNET?

Bar magnets are permanent magnets, they can't be switched on and off, they always have a magnetic field. They have two poles: north (positively charged) and south (negatively charged). They attract metals such as iron, steel, cobalt and nickel. They also attract and repel other magnets.

Bar magnet. Photo taken by Aney, 2006-03-12, GFDL via Wikimedia

WHAT DOES A MAGNETIC FIELD LOOK LIKE?
We can see the magnetic field of a bar magnet using iron filings.

By Alexander Wilmer Duff [Public domain], via Wikimedia Commons

HOW DO WE REPRESENT MAGNETIC FIELDS?
We draw lines from the north pole to the south pole of the magnet. There are more lines and they're closer together near the poles because the magnetic field is stronger there.

WHAT HAPPENS WHEN TWO MAGNETS ATTRACT OR REPEL EACH OTHER?
Look at the pictures:

Two magnets repelling. By Geek3 [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

Two magnets attracting. By Geek3 [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

HOW CAN WE IDENTIFY A MAGNET?
Magnets repel other magnets, but they don´t repel other substances.