You can combine two or more table cells located 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 that you want to merge.
- Under Table Tools, on the Layout tab, in the Merge group, click Merge Cells.
- Click in a cell, or select multiple cells that you want to split.
- Under Table Tools, on the Layout tab, in the Merge group, click Split Cells.
- Enter the number of columns or rows that you want to split the selected cells into.
The video above has been made me by me and the text is from a Microsoft Blog