How to play electric guitar and use a mic ?

All very well playing live with one instrument or singing with an Acoustic guitar not plugged in to the mac. I can play the guitar through the jack on the 13 inch MBP and use head phone to listen using a slitter.

I can plug my USB mic in and use that, But not both together.

Anyone got any sugestions to how this can be done????

I want to play live with my electric guitar through the mac on FB or you tube and sing using a mic.

I cannot do it analog using an amp as it makes to much nose. I can only do that when no one is in , or i am using the accustic. . So how do i set up the electric guitar and a usb mic through garage band to play live?