DNS stands for Domain Name System and primarily it translates easy to remember addresses such as www.cultrix.co.uk into the actual location of the resource (in this case, a website) which actually resides at 126.96.36.199 (much less memorable!). As well as this, DNS also governs things like where email should be delivered for a particular domain; so if you send an email to ITExperts@cultrix.co.uk, your email server first uses DNS to find out, "Where does email for cultrix.co.uk need to be delivered?".
Whoever is responsible for managing your IT infrastructure generally likes to keep control of managing your DNS. This is normally done in a control panel by someone with the technical known-how. DNS management can be done in the control panel provided by whoever is hosting your domain name - this will be the company you pay the domain registration fee to annually or biennially (or possibly longer: you can pay for up to 10 year periods at a time). It could also be done in the control panel provided by your email and/or website hosting company. Both work perfectly fine and it's just down to preference.
If Cultrix provide your domain, website or email hosting then we can provide you with a control panel to manage your DNS, or we can make changes for you on request. If your DNS management is provided by a different domain or email/website host then Cultrix will happily manage your DNS for you under an existing IT support agreement, or on an incident basis under a Pay As You Go agreement.