Can you please indicate what is unclear in the README?

$ perl ./geoip --fetch --DB=dbi:SQLite:dbname=geoip.db
[download]

Will do everything for you if you have a working DBD::SQLite.

A demo:

$ ls -l geoip.db
/bin/ls: cannot access 'geoip.db': No such file or directory
Exit 2
[download]

Be patient on the next one, it'll take a while to finish (my demo took 5 minutes). You will need enough memory and disk space. My process took 13 Gb of ram.

$ perl ./geoip --fetch --DB=dbi:SQLite:dbname=geoip.db
Create table stamps
Create table continent
Create table country
Create table ipv4
Create table provider
Create table city
Create table ipc4
     2020-06-22 21:16:39   4689345 GeoLite2-ASN-CSV.zip
 304 2020-06-22 21:16:39   4689345 GeoLite2-ASN-CSV.zip
     2020-06-16 13:13:32   1805947 GeoLite2-Country-CSV.zip
 304 2020-06-16 13:13:32   1805947 GeoLite2-Country-CSV.zip
     2020-06-16 13:19:50  41827687 GeoLite2-City-CSV.zip
 304 2020-06-16 13:19:50  41827687 GeoLite2-City-CSV.zip
Reading Country       info ...
Reading Country  IPv4 info ...
Reading Provider IPv4 info ...
Reading City          info ...
Reading City     IPv4 info ...
[download]

$ ls -l geoip.db
-rw-r--r-- 1 501100544 Jun 25 00:30 geoip.db
[download]

So there you go, 501 Mb of SQLite database.