shift+Enter: run this unit (the currently selected unit), select the next unit
Ctrl+Enter: Run this unit (the currently selected unit)
Alt+Enter: Run this unit (the currently selected unit) and insert a new unit under it
Y: This unit (the currently selected unit) is transferred to the code state
M: This unit (the currently selected unit) is converted to Markdown state
A: Insert a new unit above this unit (the currently selected unit)
B: Insert a new unit below this unit (the currently selected unit)