Look, things should be like this:
1. Have an internal DNS responsible for your internal network, configured with the dns address provided by your ISP.
2. Have *only* 1 DHCP server in your network (use several server only in complex networks, with special configurations), configured to dynamically update DNS. All your server must have manual IP, and be left out of your DHCP scope (Set the scope like 192.168.1.10-192.168.1.253), and give your servers IP's from 192.168.1.1 to 192.168.1.9, and usually your router 192.168.1.254. All others network equipments (printers, network scanners, access points) must be set up to use DHCP, but all of them should have a reservation in the DHCP server.
You don't need to manually add anything. (only the reverse lookup zone in the DNS, but you don't need it unless special conditions). Once the DNS is set up, every computer configured to use that DNS will update itself with A records in the DNS. Also, when DHCP hands out an IP, it should automatically update DNS.
Now, if you configure a computer in your network to use another dns server (the dns supplied by the ISP for example), your DNS will not see that computer, will not update it and problems will begin. Also, if you don't configure the DHCP to dinamically update DNS, same problems will happen.
Now, many new network admins panic when installing DNS because they don't see it updating. The thing is that it really takes some time, depending of the size of your network. Could take15 minutes, 30 minutes or maybe more for hosts starting to update in DNS. Also, many hosts update after 2 days in that host is powered down for 2 days, for example. And when they panic, they start messing up with the settings, manually updating and so on.
There is really nothing more to it. As long as you do everything right, it's all starting to work smoothly. But many problems appear if you use on some workstation another dns server, or if you don't configure your dns server to point to itself at the dns setting in IP settingon the NIC, if you forget to set DHCP to dynamically update, or other small mistakes that can cause trouble.