Sorry for the song I thought it was the song that people used a lot, I heard song similar to this very often so.
For the lag, it might just be my browser. So I would recommend adding a downloaded version of your game for people who have laggy browser like me. And jump buffering is basically a timer after you press space bar. For example 0.1 second. If you press space bar 0.1 second before hitting the ground you will immediately jump when landing , even though you didn't press it on the ground.
Thanks for responding this long lmao.