Every permanent magnet has two poles, named north and south, though they could have just as easily been called A and B. Similar poles repel while opposite poles attract. It takes a lot of effort to hold repelling poles of a magnet together, while it takes effort to remove attracting poles. The most powerful magnets attract so hard that they can cause injuries by pinching skin between them.
For thousands of years, permanent magnets were the only magnets that humans had. The electromagnet was only invented in 1823. Before that, magnets were mostly novelties. Using an electromagnet, it is possible to induce a current in any ferromagnetic materials, such as an iron paperclip. The effect quickly fades, however.
Permanent magnets can be a nuisance by threatening to erase data from ATM cards or computer hard drives. A common way of erasing data from a computer hard drive and making sure it is irrecoverable is to run a magnet over it. Otherwise, "deleted" files actually remain on a computer, just hidden. This is because it is more work to have the computer actually delete the data. Rather, the data is designated as a sector of the hard drive that can be written over without concern.
