There are a few reasons why you might not be able to merge cells in a spreadsheet. One possibility is that the cells you're trying to merge are adjacent to each other, but not in the same row or column. Another possibility is that the cells you're trying to merge contain data, and merging them would cause that data to be lost.
If you're having trouble merging cells, check to make sure that the cells you're trying to merge are adjacent to each other. If they're not, you won't be able to merge them. Also, check to see if the cells you're trying to merge contain any data. If they do, you'll need to delete that data before you can merge the cells.