You see the lane at the bottom, that’s the gameplay area!
You can use your mouse and press [left click] to place the notes.

There are 5 note types, and you can use the number keys to change the note types
[1] - Tap Note
[2] - Catch Note
[3] - Release Note
[4] - Mines
[5] - Gimmick Note (Unused in-game)
Hold notes is only available for Tap Note. To place it, you need to left click, then drag your mouse to the right.

The thick vertical lines is called “Beat Bars”. Note that is placed on “Beat Bars” lands on beat
To place the note in-between beats, you can increase the bar size with the following key binds :
[A] - Decrease vertical lines inside the bar
[D] - Increase vertical lines inside the bar
