Padlock shim set:
That’s what the picture is. They are very simple, and work on most cheap padlocks. It’s just a little sliver of metal that you stick into the space between where the bolt goes into the lock (the bolt is the thing that unlocks when you unlock a padlock). All you do is slide the padlock shim down the shaft of the bolt (where the notches in the bolt aren’t), then twist. The latch that latches the bolt to the rest of the lock keeping it locked will give way, and the bolt will pop open because it is springloaded. Works great on Masterlocks. You might want to use pliers to hold the shim, gives you extra leverage and doesn’t cut into your hand. Sometimes locks have two notches in the bolt opposite each other, latching the bolt to the rest of it twice. Supposed to prevent the use of padlock shims, add extra security, no problem just use two shims at the same time!
To make these shims is pretty easy too. They’re just little slivers of metal that go in between the bolt and the lock. You can make them out of beer cans, do a google search, or rather, here’s a link Beer can padlock shim. But those suck, and are good for one usage. Go to the hardware store and buy the thinnest sheet metal you can find, that will work much better. Just cut a sheet to match the shape of the ones in the picture, and bend it around the bolt on the lock. Easy as pie.
Some well made locks have very little space between the bolt and the lock. Shims won’t work on these, as they will not fit in the space. I’ve heard of people using a very thin copper wire from RadioShack. Bend it into a U shape, and slide it in, below where the latch is. Then try to bring the other end back up where you can grab it with some leverage and yank. The hard part is getting the end you stuck in back out, so you can pull it. I’ve never had success with it (only tried a couple times, gave up and just picked the lock), but I’ve heard of people doing it.