I2P’s aim is to create an anonymous network which offers a simple network layer for applications of many kinds.
Every user of I2P routes traffic for other users. All the traffic is encrypted a few times. So all the stuff that users forward is only usable for the sender and the final destination. You are not responsible for what you route.
I2P doesn’t hide the fact that you run I2P. It even publishes your IP in the NetDB. Any service that is offered by your router has a own destination (~I2P-IP). There is not any relation between a public destination key and a IP address: You are anonymous, in technical terms.
Offcourse this comes with some drawbacks. I2P is not so fast than the plain internet. Every packet must be routed over a certain count of other I2P-participants.
You can never be 100% anonymous but I2P tries to come as close as possible to that.