I have a conductivity kit from Atlas Scientific, but the ezo conductivity module is missing. I just connected the sensor probe to pin A0 on the Arduino Uno with the analogRead command in the source code. However, I'm still confused about the sensor output. Can I convert sensor output to microsiemens/cm? If so, what is the source code?
No, before the probe is connected to an Arduino or any uC the probe signal will need conditioning. In some examples of signal conditioning the actual probe is a leg of a whetstone bridge and in some designs other circuits are used. The probes in the link have ranges and are normally checked using a buffer solution (a solution of known conductivity). Place probe in known solution, rinse, move to another known solution and along it goes. Your display and code are tuned to the probe. A Google of "conductivity meter circuits" will bring up examples including signal conditioning circuits. There is more to it than just connecting the probe to a uC and getting results.