Select the cell or range you want to copy
Press Ctrl + C
Click the destination cell
Press Ctrl + V
To cut instead of copy, press Ctrl + X, then Ctrl + V
To paste only values, use Paste Special and choose Values
To paste only formatting, use Paste Special and choose Formats
To copy and paste with the mouse, right-click the selection, choose Copy, then right-click the destination and choose Paste
To copy a formula, copy the cell and paste it into the new location
To fill adjacent cells quickly, drag the fill handle from the copied cell
To copy across sheets, copy the cells, switch to the other sheet, and paste