Open your Google Sheet
Select the cell where you want to add new cells
Right-click the selected cell
Click Insert cells
Choose Shift right or Shift down
To add multiple cells, select the same number of cells first
Right-click and choose Insert cells
Select the direction for the new cells to move
To add an entire row, right-click a row number
Click Insert 1 row above or Insert 1 row below
To add an entire column, right-click a column letter
Click Insert 1 column left or Insert 1 column right