`dig` - DNS lookup utility

dig [@server] [-x addr] [name] [type] [+queryopt...]

Options you will use

@server: ask this server instead of the first nameserver in /etc/resolv.conf
-x ADDR: reverse lookup (PTR)
+short: just the answers
+noall +answer: only the answer section, with TTLs
+trace: iterate from the root yourself, showing each delegation
+norecurse: do not ask the server to recurse
+search: apply the search list from resolv.conf (off by default!)
+showsearch: show every search-list attempt
+time=N +tries=N: timeout per try and number of tries

$ dig +short example.com

the address

$ dig example.com MX

another record type

$ dig @10.0.3.53 api.lab

ask the authoritative server: aa flag, full TTL

$ dig +noall +answer example.com

answer and TTL only

$ dig +trace github.com

root -> com -> github.com

status NXDOMAIN = the name does not exist. NOERROR with ANSWER: 0 = it exists but has no record of that type (NODATA). SERVFAIL = the resolver could not get an answer. "no servers could be reached" = nothing replied.
dig exits 0 for NXDOMAIN and SERVFAIL - it got a DNS answer. It exits 9 when no server replied.
dig does not read /etc/hosts itself, but on Ubuntu its default server is the systemd-resolved stub, which does.

Try dig in a real terminal Free, in your browser - a real Ubuntu terminal to try it in, with missions that check your work.