Almost all home routers will have their built-in DHCP server feature turned on by default. When enabled, the DHCP component will allocate IP addresses and related options (subnet mask, default gateway) to client systems configured to obtain their IP addresses automatically.
Although the DHCP component simplifies the allocation of IP addresses, you should disable the feature if you plan on configuring client TCP/IP settings manually. In fact, some advanced router features cannot function with DHCP enabled. Furthermore, most routers are configured to allocate up to 50 or more IP addresses to clients as necessary. If you plan to continue using the DHCP feature, consider changing the range of available addresses to a number that matches the number of client systems on your network for security purposes.