If you use Copy and Paste or just drag the cell frame, the existing cells
will replaced.
You can insert a column by right-clicking the column header it should be
inserted before, and then select Insert. You can select a cell in the column,
and then choose Insert - Columns from the main menu instead of using the
right-click menu. If you want to insert more than one column, select as many
columns as you want to insert, and then right-click one header and select
Insert. You can also select non-adjacent columns or cells by holding down
Ctrl and clicking them.
You can select a range of cells (or a whole row or column), drag the frame,
press and hold Shift, and the outline you are dragging around will change to
a vertical or horizontal bar with a T in each end. Position this bar between
the cells you want to insert the data between. Be sure to hold down Shift
when releasing the mouse button. The existing cells will move to make room
for the new cells. If you dragged a whole row or column, the cells around the
original cell posistion will move to fill the gap.