Wherever you can use DNS - you can use it. I have the DNS set on my SOHO Router and my entire Network is free of ads.
Every device which is connected to the SOHO Router is also free of ads. If you have e.g. your XBOX or AppleTV or whatever connected via this router all the entire Apps are also free of Ads. That's the big advantage against every existing Adblocker.
If you have a non routed device than I recommend to use the certificate because this prevent HTTPS errors. Just open a browser on your device, go to:
pki.keweon.center
and after 3 seconds the certificate download will start. You only need to install it manually. This is a 3 click process. Type a Name (e.g. keweon) click ok, ok again and it's done. No more HTTPS errors because of adblocking.
And the Android Client from frostnerd (DNS Changer within the Playstore) is working even on a non rooted device.
If you want to see what's the different between using keweon with and without the certificate than just uninstall the certificate. Than you know why it is recommended.
If you want to know what DNS Server you should use than you should ask someone from your Country or try and do. I have no clue what I should recommend for you. Take the Server which is physically next to you and try it.
If you have additional questions than feel so free and ask. There are no dumb questions.