Thank you for trying the game out!
TL;DR: if you see the red dot, it is out of sync.
If you are new to rhythm game in general I can provide some tips to you here:
1) It is all about synchronization between visual and audio components. Try to utilize the visual feedback (in this case if you see a red dot which means it is out-of-sync).
2) There will unavoidably some very brief delay between you hand movement and the visual/audio feedback(this is even true for a real string musical instrument). Try to experiment by moving ahead of audio or a little bit later or to calibrate the syncrhonization of your hand movement and the game until you don't see much red dots appearing. An advanced rhythm game will have the capability to calibrate the delay in the game settings.
Sorry that I don't really have the time to implement the in-game tutorial component. I would prioritize this next time during my game jam.