An HTTP proxy understands web requests. For a plain http address it fetches the page for you. For an https address it opens a tunnel to the site and passes the encrypted traffic through untouched, so it cannot read what you send.
Because browsers, scrapers and command-line tools all support it, the HTTP port is the safe default. On PiratProxies every plan has an HTTP port and a SOCKS5 port that reach the same addresses. For the residential plan the HTTP address is http://USERNAME:PASSWORD@resi.piratproxies.com:8080.
Read next: HTTP vs SOCKS5 proxies: which port to use