I have a device that puts out 0-5v based on what it's doing. How can I use the raspberry pi to read those voltages? I would then have scripts do whatever is needed or maybe display via a webpage. I would like the pi to log the readings every second or every few seconds, just not sure how to start.
You need an ADC (Analogue to Digital Converter).
Google MCP3008 (a popular 10-bit 8 channel ADC) as an example.
You could use the ADC built into most* Arduino and connect to it using you RPi via a python script as depicted in this tutorial