Each track has a "+" symbol at its end. Clicking it opens options to create a new block by selecting the desired type.
Selecting
Blocks can be selected with a single click on them. The currently selected block is marked with a line underneath it.
Deleting blocks
Press DEL/ BACKSPACE or right-clicking and select the corresponding option
Moving
When hovering with the mouse over a block, the mouse cursor turns into a dragging symbol. Hold down the mouse button and drag the block to place it at a different place in its track.
Duplicating blocks
Press CMD/ CTRL + D or right-clicking and select the corresponding option
Copying blocks
Press CMD/ CTRL + C or right-clicking and select the corresponding option
Cutting blocks
Press CMD/ CTRL + X or right-clicking and select the corresponding option
Pasting tracks
Press CMD/ CTRL + V or right-clicking and select the corresponding option