Merging cells in Excel 2013 is a convenient way to add titles or column headings to organize and clarify the data in your worksheet. Merging is more often done vertically, but it is also possible and useful to merge cells horizontally using the same process.
Select the range of cells to merge. Click in the first cell, hold down the mouse button while moving the mouse over or down to the last cell to be merged, and then release. On the Home tab, click “Merge & Center” in the Alignment group if you would like to center information such as a title or heading in the merged cells. If centering is not desired, click on the Merge & Center down arrow and select “Merge Cells.”
To unmerge the cells, place the cursor in the merged cell, click the "Merge & Center" down arrow and select “Unmerge Cells." The cells return to the single-cell format, but if Merge & Center was initially selected, the centering formatting remains. To return to the left-aligned, original formatting, place the cursor in the relevant cell and select the “Align Text Left” icon in the Alignment group on the Home tab.