The first thing you need to do is gather your tools. You can purchase a lock pick or make one yourself. There are plenty instructions online for making a lock pick or places to buy one. There are also some videos on YouTube that tells how to make a lock pick. Just search for "How to make a lock pick" and you will see several. It is just easier to buy one yourself. Lockpicking sets usually comes with all the materials you need including a tension wrench.
Now that you have your tools, get a padlock to test this on. Turn the lock upside-down so that the keyhole is facing you.
Stick the tension wrench into the bottom of the keyhole. Use your finger to keep it in place and to apply just a little pressure to it. Don't use too much pressure. If you do, this will not work. Also, make sure you are keeping the same amount of pressure through this whole procedure or you will have to start all over.
Get the right-sized lock pick and start working it into the keyhole. With the lock pick, push each of the little pins inside the keyhole upwards until all of them have been pushed. That is it. You've just picked your first master padlock.