As already mentioned by @David Ruess, if the DHCP server is sitting on a different VLAN or a remote site then you need to configure DHCP helper. DHCP helper will act as a relayer. For instance, say if an endpoint in VLAN 10 is trying to get an IP address and the DHCP server happens to be located in VLAN 20, in that case the broadcast traffic sent by the endpoint in VLAN 10 will be converted to unicast traffic by VLAN 10 gateway (could be an SVI on the switch) and sent to the DHCP server. However, this will only work if VLAN 10 gateway has the DHCP server configured as a DHCP helper.