RLV basically is a tool to interact with the viewer from scripts (even though it originally has been invented for very specific purposes).
The RLV folder is just a folder at the top level in your inventory, i.e., directly below "Inventory", which must be called #RLV. This is the only folder in your inventory that RLV can interact with.
If it doesn't exist yet, just created it manually.
When you're using an RLV-enabled viewer, it will show with a special symbol, indicating that it is a system folder.