sir, please tell us the shortkeys for new cells
Esc+B ,Esc+A , Esc+M,
Esc+B to insert new cell below
Esc+A for insert cell above the selected cell
Esc+M for markdown below
Esc+X for deleting a cell
You just have to go to Help in your already running jupyter notebook,select keyboard shortcuts and find all useful and handy shortcuts.
Just click on any cell in jupyter and press BB for new cell below selected sell or AA for new cell above the selected sell. If selected cell is in editing mode then press esc key and try the above shortcuts.