To see how magnets push and pull each other, get out your wooden Brio trains. One end of each car has a positive magnet and the other end has a negative magnet. If you try to match up two positive magnets or two negative magnets, they will push each other apart, but if you match a positive and a negative, they'll pull together, letting the engine pull the freight cars.
Magnets will only pull on things that have iron in them, because only iron atoms will line up to become temporary magnets, attracted to other magnets. Take a magnet (your Brio train will work) and go around the house seeing which things have iron in them. If you try things made of copper or zinc or aluminum, you'll see that they are not magnetic even though they are made of metal.