On top of the manual, there is also the VLAN tutorial by @pcunite. If these resources are not enough to answer your questions, give a detailed description of the desired configuration (vlan <=> port mappings, subnet <=> vlan mappings etc.).
A dhcp server needs to be
- linked to an L3 interface with an assigned IP address
- linked to at least one address pool configured under /ip pool
- enabled
In order that the clients would get a useful configuration, an /ip dhcp-server network item must exist, linking the subnet address to parameters like default-gateway, dns-server etc. So whenever the server leases out an address from a pool or a static lease, it matches the address against these items, and provides these parameters found in a matching item in its DHCPOFFER and DHCPACK sent to the client.