Merge table cells into one cell
You can combine two or more cells in the same row or column into a single cell. For example, you can merge several cells horizontally to create a table heading that spans several columns.
Select the cells you want to merge.
Note If the cells in your table have no visible borders, you may find it helpful to show gridlines. Click Table Tools > Layout > View Gridlines.
Right-click the selected cells and click Merge Cells.