This example would add the Unified hosts + fakenews + gambling + social block list from GitHub StevenBlack/hostst:
/ip/dns/adlist
add url=https://raw.githubusercontent.com/StevenBlack/hosts/master/alternates/fakenews-gambling-social/hosts comment="GitHub stevenblack/hosts - Unified hosts + fakenews + gambling + social list" ssl-verify=yes
For a list of some IP blocklists, see IP-Blocklists page.