Uart is just serial, you’d connect it to your serial pins on the pi and read serial from Linux like normal. Data is whatever the protocol Honeywell is using. Could be any range of things sent in a predictable pattern. Could be timestamp,temp,air quality,status, and then some kind of delimiter like newline or eor. Note the pi devices use 3.3 volts instead of 5 so you have to make sure Honeywell is not sending too much voltage as a logical high. There’s probably an easy way to convert it though using a voltage devider.
Minor clarification: UART is “just serial” but when people say “serial” they usually mean RS-232 or RS-422, and these don’t use 0V / 5V like you would for 5V logic. They use anywhere from 3-25V signals, with positive voltages for zeroes and negative voltages for ones. Your PC, if it has a serial port on it, probably sends around +/- 13V (this is typical, IIRC).
So don’t hook up 5V logic parts to a serial interface. If you look at RS-232 interface chips they have integrated charge pumps and external capacitors to generate the Tx voltages from Vcc.
How much do those sensors cost?