If you connect the source of an N-channel Mosfet to +12V then the load must connect to a higher positive voltage.
The gate will be +12V when the Mosfet is turned off and the gate of this Mosfet will be +17V when the Mosfet is turned on.
If you connect the source of a P-channel Mosfet to +12V then the load must connect to a lesser voltage, usually 0V.
The gate will be +12V when the Mosfet is turned off and the gate of most ordinary P-channel Mosfets will be +2V or 0V when the Mosfet is turned on.