Can you post a link to your load cell?
The meaning of 1mV/V -- at rated load , the load cell will output 1 mV signal when the excitation voltage is 1V. Thus if you apply 5V excitation, the load cell will output 5 mV signal at the rated load.
The load cell is compatiable with the HX711 Module which contains a high gain amplifier and a 24-bit Serial ADC.
You can operate your system in one of the following two ways:
1. Use of the HX711.h Library which determines the calibraton factor in order to determine the unkown weight.
2. Make a 2-point calibrartion of your load cell and then measure the unknown weight.