If you want to use the list manually, or from custom software, you should instruct your system to do a dns query for the information. For example, if you want to check if 188.8.131.52 is on the blacklist, you might type this at the command-line:
If you get back an IP address (typically 127.0.0.2), then the IP you asked about is listed. If you get back a non-existant message, then the IP you asked about is not listed.
"nslookup" is just the most common method for looking up a hostname. Your system may have another name for it. Other common names are "host" and "dig".