Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
This build simply allows you to get the upper hand in the game early, considering that will be what has to be done because shaco is a squishy character. Once you start with your boots and your potions you select two poison shiv as your first skill,(if it is 3v3) you're going to wanna keep spamming two poison shiv. You will be able to do this because you'll have your mana potion. If you keep playing like this you should be able to conjure up a kill sometime soon, and eventually once you get enough money and get your manamune, it help you spam your poison shiv and increase your attack enough for you to do real damage. If you just keep following this build sequence the rest is self explanatory. Although, if you are using this build for 3v3 you wanna replace ghost with flash.