IPv4, or Internet Protocol version 4, is a networking protocol that maps 32-bit IP addresses to devices on a network. IPv4 routes most of the network traffic on the internet.

IPv4 addresses are 32-bit integers conventionally written in dot-decimal notation, like

IPv4 Articles

Attaching a public IP makes your compute machines addressable over the internet.
Send outbound traffic from your Droplet over a reserved IP address.
Disable IPv4 to rely solely on IPv6.