The function has been available on Apple iOS for a long time: the “Swipe to Queue” gesture allows you to quickly add titles to your playlist – just with a swipe. However, the function has never been available on Android.
In the meantime, however, the streaming provider is already distributing them to selected users. Broader distribution is expected to start within the next few days.
So far I haven’t been able to use the function in the Spotify app on Android. I just checked again. Ultimately, you can play a song via Spotify, then browse the app and swipe right on another song – that song should then end up in your playlist if you already have Swipe to Queue.