OWIN and KATANA

Hye Dear, Can you help me please to understand the concept of OWIN and KATANA in asp.net. Why we need it? Before OWIN and KATANA what was happened? After owin what the ease we made. Where we can use owin and katana. Why authentication is self host? what is the benefit of authentication self hosting. I'm really confuse about these kind of things. Thanks in advance,