There is a rather useful document on DNS from 123-Reg called DNS Management Guide, which is well worth a read if you are new to DNS for internet domains.

You can use DNS servers as a way of filtering content on your network. Clearly this can be bypassed with a VPN but as basic home filtering and protection it is a reasonable option. One such service is Norton ConnectSafe.

One of the drawbacks of traditional DNS is that it is done in "plaintext", which is another way of saying it is not encrypted and hence a security/privacy leak. This is where DNS over HTTPS comes in, both Firefox and Windows have started to introduce this.