If you need to fill cells with sequential text such as months of the year, days of the week, or text plus a number such as Quarter 1, Quarter 2,…, use the fill handle to quickly create labels for the cells simply by typing the first item in the series.
For example, you would type January in your first cell, then hover the mouse over the bottom right hand corner until it turns into a black cross, then click and drag the fill handle from the cell containing January until you have all the monthly labels you need.