DNS - please for information

[incognio]

Hello
Please if someone can give me more info (in accessible language) about DNS servers.
I'm searching everywhere but the only one I find is that DNS transforms the domains into IP addresses.

Yes, this info is simple and useless for me.
Also I know in the DNS there is records with types A, MX, CNAME and more which points to IP address.
I have make "A" and "MX" DNS records from cPanel but I don't ask my questions as user.

One domain needs atleast 2 name servers. People say that they have to be on diferent internet service provider -
If one of the ISP's is not available the other should be online.

If I have two name servers and one webserver with cPanel
Let call them NS1, NS2 and webServ
In DNS there will be "A" record pointed to webServ's IP

If NS1 and webServ use same internet provider (ISP1) and NS2 use other - ISP2

My question is:
How this will be useful for me if ISP1 get disconnected. In fact only NS2 will be working online but in this case webServ will not work because it use ISP1 which will be down.
And when NS2 is online its A records will show that have to be opened webServ's IP and it will not work.

Other questions:
Is it posible to keep my internet connection awalys on with Primary and Secondary internet provider? And how?
If webServ is connected with two ISP's - two ISP's have diferent IP adresses. If ISP1 is down - webServ will be accessible trought the other IP of ISP2 but I think this is not the decision.

I think you understand what I mean.
Sorry for my bad english.
May be I don't ask the questions correct but I think you understood my idea and what I mean.

[oshs]

Nameservers running off the same server as the website have no redundancy, i.e. if the box goes offline so does everything else.

And even if you have external nameservers, if your web box goes down, then they are not going to bring it back up. However when it does come back up, they will return your website to being visible instantly as the DNS never went down.

Some nameservers are required to be on separate servers, such as .de domains. However .com and .co.uk nameservers can be hosted on the same server.

The real benefits of external DNS servers are when you have multiple Cpanel servers sharing a set of nameservers.