Please share information that you get from your GPS or an example of what you're already trying.
You need at least two program routines: one to use the ASCII port control instructions to bring the data into the controller, and one to use the ASCII parsing instructions to pull the data values out of the string.
Let's take an example of an NMEA sentence:
$GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47
The MicroLogix serial port in ASCII protocol mode can watch the incoming data string for one or two Termination characters. The default terminator is 0x13 hex (carriage return) because that's a typical end-of-line character in ASCII.
If you make the Termination character the asterisk (0x2A hex), you can use the ASCII Read Line (ARL) character to bring in everything from the $ to the *, then immediately use an ASCII Read (ARD) of 2 bytes to get the checksum.
After you have the NMEA0183 sentence in a String datatype, you can search through it using the ASCII String Search (ASC) instruction. Every time you find a comma, you save the position and use the ASCII String Extract (AEX) instruction to pull out the values.
I'm not an ASCII handling expert but I'll see if I can give you an example.