What one person thinks is easy another may not
In this instance middle of the circuit outlet is your exisitng outlet
Garages require GFCI, so this could be different
Shut off power 1st - verifiy oit is off
You connect a new wire, & then connect to the new outlet
But codes do vary by area on what is required & the specifics of how to wire
Specifics depend upon your situation & existing wiring & codes