[Closed] Free virtual trainers for use with turbo?

I picked up one of the Elite fluid turbos that were / are on offer at £99 at the moment, and have a speed / cadence sensor on my bike that I use when riding on the roads.

Having never used anything like Zwift etc before (and I won't be doing until January as I'm not allowed to unpack the turbo until Father Christmas has visited...), are there any viable free options for these sorts of virtual riding arrangements? I'm reasonably happy enough just to sit and spin in the house watching a few films etc, but I quite like the sound of the Zwift / Trainer Road type things, but can't really justify an outlay being a skinflint.