Thanks to DHCP, when a laptop or phone joins Wi-Fi it automatically receives an IP address, the internet gateway and the DNS server address — nothing needs to be typed in by hand.
DHCP usually runs on the router or a server. When configured properly, each network (VLAN) has its own address range and address conflicts do not happen.
Example
A new employee connects a laptop to the office Wi-Fi and the internet works immediately — that is DHCP at work.