As with Excel, a Google spreadsheet can have automatically fill a series of cells - e.g. months of the year, sequential numbers, football teams and almost anything else!
To paste sequential values into your spreadsheet, you will need to have two cells that show the sequence. For example, if you need to paste the months of the year in the first column of your spreadsheet, enter January in A1 and February in A2. Then select both cells, hover over the small blue box in the bottom right of the last cell selected (until a cross appears) and drag your cursor down the number of cells you want to create - in this case it will be A12 to add the remaining months. This works in either columns or rows.
This tip works with numbers as well - in fact it works with any sequence you need. If for instance you wanted to have a list with dates set 7 days apart, add the first 2 cells as dates 7 days apart and use the drag to populate more cells - the dates will be 7 days apart each time. You could also use it to add just even or odd numbers.
Even more impressive is to start a series of "things" like countries, football teams, colours or whatever - and hold the Ctrl key as you drag to fill - the series will be magically generated from thin air!