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 is a top laning Shen build, built around the concept of trapping your enemy, slowing them down, and preventing them from escaping your icy grasp while you beat them down.
I explain the item/slow redundancy choices in the item notes.
Feel free to play around with it and leave your recommendations!