Hello, this question is not actually about providing hosting service but that's the part where I got stuck.

I want to code an e-commerce website and sell it to clients. But not like giving codes, but like providing software as a service.

So they will sign up, pay, provide a domain name and in a short-time they will have a full functional website.

How should I do this? I can create subfolders for every user and make them use it like( www.eralpssite/username/ )

But of course I want to be able to direct the domain's they provided to their websites. So what should I do ? Are nameservers for this case? I mean if www.usernamessite.com entered route it to the folder www.eralpssite.com/username/

And how hard would it be programmatically to buy new domains and set their nameserver to my nameserver. I mean if they have their own domain they can login where they bought it and set the NS to my NS but if they want to buy a completely new domain they will state it in the options and my website should be buying that domain, how is this process?

My post could be a little bit messy since I am not very experienced with these kinds of things, I generally do desktop programming ^^

Regardless of what type of OS you are using (Linux or Windows) this is rather simple to do and requires zero programming, just some configuration on your end.

Your clients will update their provider of their domain (i.e. GoDaddy.com) to have all www.usernamessite.com to go to a specific IP address (your hosting server).

On the hosting server, you would set up virtual websites. On a windows PC, this is done in IIS by right-clicking on the Web Sites folder and the 'Add new web site'. At some point, it would ask you to enter in the host name, which would be www.usernamesite.com. You can have multiple ones listed here.

On Linux, you would create a configuration file for apache and specify the host name using the ServerName entry.

It's really easy to do and you just need to do some reading on it. Again, it's all configuration and zero programming.