Hello!
First, is it clear to you that you can host as many domains ("websites") as you want using just one, shared IP address? Using a dedicated IP address for a domain is just an option, a choice you can make but it is not necessary.
Given the above, in Tools&Settings=>Tools & Resources=>ip&addresses you just declare which are the additional IP addressed of your server (beside the main, shared, IP address)
Then to assign a particular domain an IP address, you must go under that domain management page, click on "Web Hosting Access", and there you'll see a drop-down to select which IP address to use for that domain (either the shared one or one of the additional IP addresses you have configured for your server)