I imagine Shipt will be operated by regular independent contractors (anyone with a smartphone like Uber, Lyft or Amazon flex). Target is just going to benefit from the proceeds of the program and likely promote it to our current clientele of guest.
Amazon has a program where drivers (who don't work for amazon) drive up to warehouses pickup packages and deliver them. Amazon's product is delivered but the drivers are more mobile, cost less than regular delivery drivers and use their own cars and gas.
Shipt will be these same people picking up stuff at Target, delivering them and Target saving money on it.