The first thing that is needed is to merge (join) the individual cells together by selecting the cells and clicking the Merge button on the Design section of the ribbon (It is like the cell merge option in Microsoft Excel). The merged area is then changed to a cell.
By pressing the merge button again, this will un-merge the cell.
Instead of pressing the Merge button you can use the shortcut key F4. All shortcut keys can be found by pressing the Shortcut Keys button on the Help Section of the ribbon
The size, in terms of grid cells and actual dimensions of the created cell, can be viewed in the right hand corner of the screen as the grid squares are selected.
If there is data text inside the cell, it is always a good practice first to reset it by pressing the Reset button on the Design section of the ribbon BEFORE un-merging the cell.