Use the Del key or Edit → Clear → Contents to remove the text, value or formula from selected cell(s), row(s) or column(s) without affecting anything else.

To delete everything in the selected cell(s), row(s) or column(s), including comments and special formatting, choose the All option from the Edit → Clear menu or from the pop up menu you get when you right click on a selection.

To remove selected row(s) or column(s) completely, use the Delete Rows or Delete Columns options from the right mouse button pop up menu.

If you select a cell or cells and choose Remove Cells... from the right mouse button pop up menu, you can then choose whether other cells in the worksheet will be moved up or to the left to fill in the space left by the cell(s) you have chosen to remove.

If you want to insert new, blank, row(s) or column(s) into the sheet, select row(s) or column(s) where you wish the new row(s) or column(s) to be placed and choose the Insert Rows, Insert Columns option from the right mouse button pop up menu.

You can insert new cells into the worksheet by selecting the area where you want them to appear then choosing the Insert Cells... option from the right mouse button pop up menu. You will then be asked whether the existing cell(s) in the selected area should be moved down or to the right to make room for the new ones.