Glad you’re up and running. Note that, volumes aren’t free (iirc). Fly doesn’t charge upto $5 anyway (ref), so that’s there too.
Yes, there’s a ~6G partition (/ as ext4) for your docker image to inflate into, and a separate boot partition (as ext2?). Both these partitions are ephemeral, as in, they don’t survive app restarts.
Fly Volumes are “persistent” (survive app restarts but not host failures, though there exists daily automated snapshots which expire in 5 days) that get mounted (as specified in fly.toml) into your app’s VM. You’d use it typically to host a database or objects and such.