I have a question, I already have a dedicated server and have to create a VPS on it, but is there any way I could do to assign different IP addresses on every VPS I make for free or without requesting more IP addresses on the provider?...
NAT stands for Network Address Translation. It allows you to map one IP address to another (ie 188.8.131.52 to 184.108.40.206). Some of the more advanced NAT techniques include masquerading (where you hide multiple private IP addresses behind 1 public IP) and PAT - Port Address Translation, where you map on individual port numbers.
Consider you have a host with 1 IP (220.127.116.11) and behind it you have 10 VMs (192.168.1.1-10). You can use PAT to forward port 1111 to 192.168.1.1:22, 2222 to 192.168.1.2:22 etc.
This would allow you to SSH to any of those hosts directly by using the port number assigned to each one, for example.
No worries. For those VMs, you'll need to have some Private IP addressing which virtualbox provides via the NAT adapter. In fact if you configure each of those VMs to use the NAT network adapter, VirtualBox will automatically assign IP addresses to them. See this section here: