A lot of stuff in that post
SSH (secure shell) is simply a way to connect to a machine remotely, to securely access the terminal on a server, a linux machine, or even a router. SFTP is secure FTP, just transferring files over SSH. Next step would be to install some kind of Linux environment and learn that, look up nmap, top/iotop, and such command-line tools, connect to your router or NAS via ssh and poke around. Linux command-line is very powerful, just there is some learning curve. Coding shell scripts may not be fun, but is useful.
DNS is just the domain name system, DNS translates domains/hostnames/URLs to IP addresses. There are different types of DNS servers, some cache information to speed up later repeat access (your ISP's nameservers), others are authoritative/primary servers for some domain, etc. DNSmasq (masquarading) is used in small networks to provide DNS locally, it is also a DNS caching service on some linux boxes.
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