I highly recommend doing to on a PC or Mac. Doing this initially on a phone is buggy. Essentially Streamio is just a player like VLC, but has the ability to have add-ons. These add-on doesn't need to be resetup on each device you install it on. Just sign in and it's working.
As for real debrid, I would pay the 180 days one because they give you points that you can redeem for another month or so of days.
Good luck.
Stremio Setup Guide
Part 1: Stremio
For Windows/Mac users - Go to https://www.stremio.com/ and download the relevant client for your platform
For Android users - Install Stremio through the Google Play Store: Stremio - Apps on Google Play
Choose a package and subscribe. I found that using Amazon Pay as the payment method is the most convenient (if you have an Amazon account)
Part 3: Torrentio
Go to Torrentio Lite - Stremio Addon
Towards the bottom of the page, select the "Debrid Provider" option and select "Real Debrid" from the drop-down menu. This will cause a new text box to appear underneath.
In the Debrid Options menu: Check the box "Don't show download to debrid links" and leave the other boxes unchecked.
Click "Install" at the bottom. It should open the Stremio app and prompt you with an "Install Addon" window. Click the green install button at the bottom.
Optional but highly Recommended - In Stremio, click the puzzle piece in the top right to view your addons. Click "My Addons" and uninstall the "WatchHub" addon. It's an eyesore and it clutters your streams list.
Now that you have completed the setup, you may install Stremio on any device of your choice (excluding IOS) and log in to your account to start streaming Movies/TV. Refer to the section below for Stremio installation on FireOS devices (Fire Stick, FireTV).