Only the host can import characters, so you have to talk to the host for getting his email address, transfer your saved game with your character with a USB-stick from your PS3 to your PC and attach it to a email to the host.
The host then has to save the attachment on a USB-stick and then transfer your saved game to his PS3.
Then the host can import your character and select you as the only one who can use it in the game he is hosting ... much too complicated for most players which doesnt seem to be intelligent enough for understanding how this works.
MfG, MEX