Press Shift and click Right mouse button.
This works for automation node, sound object, plugin, track, block, note, etc.
Select/unselect something:
Press Ctrl key and click Left mouse button.
Zoom in or out:
Press Ctrl key and use the Mouse scroll wheel.
Scroll vertically:
Use the Mouse scroll wheel.
Below the timeline area in the sequencer you also need to hold a Windows / Cmd key.
Note that the editor works differently. In the editor, the mouse scroll wheel does the same as Arrow Down and Arrow Up.
Scroll horizontally:
Press Shift and use the Mouse scroll wheel.
Note that the editor works differently. In the editor, the mouse scroll wheel does the same as Arrow Down and Arrow Up, and those keys will by default zoom lines in/out, or move the cursor 8 steps up/down, depending on which Shift key is pressed.
Play song
Use the Mouse scroll wheel inside the sequencer or in the bottom bar timelines.
Move the mouse cursor and Scroll up to start playing / Scroll down to stop playing. (Note that this behavior can be configured under Edit -> Preferences -> Sequencer)
MacOS notes
Alt is often called Option on an Apple keyboard.
Pressing Right Cmd is the same as pressing Right Ctrl.
If you want to swap Cmd and Ctrl, select Swap Ctrl and Cmd under Edit -> Preferences -> Gui. This will swap Cmd and Ctrl for both mouse operations and keybindings.