A record
A DNS record that maps a domain or subdomain to an IPv4 address. The most basic 'point my domain at this server' instruction.
Format
example.com IN A 192.0.2.10 tells resolvers that requests for example.com should hit IP 192.0.2.10.
TTL
The Time-To-Live value controls how long resolvers may cache the record before re-asking. Short TTLs (60-300s) make migrations fast but increase DNS load.