Cross File VLookup allows you to cross correlate two sheets. Select the column you want to match on in the first sheet, and then select the sheet to search and its column. Gigasheet will add a new column to the original file with true (when a match was found) or false (when no match was located).
For example, say you have a log file with a column of IP addresses, we'll call it My.log and a second file that lists bad IPs, we'll call that one bad-ip-list.csv. You'd run Cross File Lookup on the IP column in your My.log, then select the bad-ip-list.csv file, and the column which contains the bad IPs, Malicious IP in this example.