can i have some example of what are these "so called" Bitcoin Banks? never heard about
These are services who offer you some interest rates of you loan out your Bitcoin to them.
That means you lose the control of your coins because you don't own the private key anymore.From this moment on it's all about trust.
I highly advice everyone to be very careful with such services.The risk of fraud is pretty high.
Bitcoin was not created to give control of your coins to a third party!!