Drag any number field this way to change it. Shift drags finely, Alt/Option coarsely. A click without dragging lets you type.
Above the rack keeps sequencers in their own area at the top, whatever the rack order. In the rack puts them among the devices.
The MIDI controls in the Control panel (clock, MIDI Learn, mappings). Its key hides and shows it too.
What the player (P) shows. The beats come from the transport, so flashes land exactly on them.
Deleting a track (its key, Delete, or its right-click menu) asks first. Untick to delete straight away.
Click a key, then press the new one. Esc cancels, ⌫ leaves the action without a key. Keys don't act while you type in a field.