Question

Which button help to select all the cells at a time ?

Answer 1

Click the Select All button.

Press CTRL+A.
Note    If the worksheet contains data, and the active cell is above or to the right of the data, pressing CTRL+A selects the current region. Pressing CTRL+A a second time selects the entire worksheet.

Tip    If you want to select all cells in the active range, press CTRL+SHIFT+*.

Answer 2

CTRLS+shift button help to select all the cell at the time