What are the 3 main differences between katana for samurai & ninja? How Ninjato were actually used!

When you imagine a katana, the Japanese sword, you would probably imagine a samurai wielding it. However, there is one more famous icon that seems to have used the katana too. They are the ninja. But when you take a look at katana held by the samurai and ninja, you can understand that they have different figures, and are carried differently too. But how are they actually different?