If you wish to enter data on many cells at once in one go, follow the below steps:-
1) Select the range in which you need to enter the data
(you can use Name box above column A to select the range in one go e.g., if you wish to select a1:g10, type the same in the name box and press Enter)
2) With the selection in place, enter your text in any of the cell
3) Press Ctrl + Enter
You will see that the same data has been entered in all of the cells in selection.