Select cell contents in Excel

Select one or more cells

Click on a cell to select it. Or use the keyboard to navigate to it and select it.
To select a range, select a cell, then hold the right bottom edge and drag over the cell range. Or use the Shift + arrow keys to select the range.
To select non-adjacent cells and cell ranges, hold Ctrl and select the cells.

Select one or more rows and columns

Select the letter at the top to select the entire column. Or click on any cell in the column and then press Ctrl + Space.
Select the row number to select the entire row. Or click on any cell in the row and then press Shift + Space.
To select non-adjacent rows or columns, hold Ctrl and select the row or column numbers.

Select table, list or worksheet

To select a list or table, select a cell in the list or table and press Ctrl + A.
To select the entire worksheet, press Ctrl + A + A. Or use the Select All button at the top left corner.

Source: Microsoft