To configure an SMP server to forward its data to another SMP server, you need to first set up the receiving server. See Configuring Standalone Replication. As per the documentation, you are instructed to click on the Add button to add your receiving server. You have noticed that when doing this, there is a box for entering a Replication Web Site.
ITMS 8.7+
N/A
The Replication Web Site is something used for hierarchy and can be safely ignored. By default, after a successful installation of the product, you will have a server entry for your SMP server listed. For example, in the following screenshot:
Notice in the example above, the Hierarchy Role says None. Therefore, when you manually add a server to receive data from the SMP server using standalone replication rules, you can safely ignore this Replication Web Site dialogue box and just leave it empty.