Roon ARC is additional and optional software. Prerequisit for it to work is an installed and working Roon system (a Roon Server and a Control for access/setup). Did you already get strated with Roon?
Welcome to the Roon community! We’re excited to have you here and ready to help get you squared away with Arc. @BlackJack is correct in that before using Arc, a proper Roon Server and control device are required.
Based on your account, I see that you’re running Roon Server from a Macbook Pro - that should definitely suffice! It’s good to note though that if your laptop goes to sleep, it will cut the connection to Roon and you won’t be able to connect using Roon or Arc from your mobile device.
Another good next step here is to review your Roon Settings > Roon Arc, share a screenshot including the advanced settings if possible.