Bo shuriken are long cylindrical pieces of iron that are also used as throwing implements, a little different from the shenban, or flatter shuriken. And they come in varying lengths, some longer and some shorter than others. I'll just demonstrate the basic throwing motion up here against an attacker.
Basically, you just want to hold it in your hand between your index and middle finger and press your thumb against the shuriken, and then just like you're going to do a shuto strike, you want to just do the same motion as you would in a strike. Over time you get an idea of distance and how the actual shuriken falls as it moves at different distances, and you're able to pinpoint with better accuracy that way. Just a little bit about the bo shuriken.