Start Microsoft Office Excel and create (or open) the file. To highlight the table boundaries, refer to the "Font". Click on the icon for a thumbnail in the form divided into cells of square and choose which method should be decorated border of your table.
If you incorrectly calculated the desired number of columns, insert a new column in several ways. Install the mouse cursor in the cell to the left of where you want to add a column. On the Home tab find the section "the Cell" and click on the arrow next to the signature "Paste". From the drop down menu select "Insert columns to the sheet". You can also just click on the "Insert" button, but it needs to be highlighted a whole column, which will appear to the left of the new column.
Another option: highlight with the mouse the column in the table and click anywhere in the right mouse button. From the drop down menu select the Paste command. Don't confuse it with the "Insert [a fragment from the clipboard]", in front of which is a special badge-miniature. If you want to insert multiple columns, select the desired number of columns, then click Insert - table will increase the allocated number of columns.
If you created a table in Excel using the tool "table" on the Insert tab, the placement of the columns on the page will expand. Select the column (or cell in that column) and move to the Home tab. Expand the menu "Insert" from the section "the Cell" and select one of the available actions: "Insert table columns to the left" will allow you to add the column to the left, the command "Insert table columns to the right" add columns, respectively, on the right. Add the specified number of columns, if you highlight the number of existing columns in the table.