Tables are for tables of data, not for layout.
You are using tables for layout, and there is no table cell to the immediate right of the vertical image.
If you are going to use tables for layout, at least do it the wrong way correctly , if you see what I mean.
Create one table. That's ONE.
A table can have many rows and many columns. You want one with, from the looks of it, with two rows and two columns.
In DW, then select the two cells in the top row and then Table, modify, Merge cells.
The insert your images one into the now merged, large top cell, and one into the cell on the left. Then you can type into the cell on the right.
Do not add a new table when what you want is a new cell. you can't add a cell at random, they have to be in a row.
If you wanted a distinct bottom row, you'd have made the ONE table with three rows, two columns, and merged the top two one the header area, and teh bottom two cells into the footer area.
BUT tables are not for layout, they are for holding tables of data. It is a great pity that DW has a control for placing so-called layout tables on the page. Because there is no such thing as a special layout table. And it leads to problems like this. Use Insert Table from the menu to have proper control over what you do.
If you start putting tables inside other tables, your code will soon become impossible for anyone to trouble shoot when they view the source code.
If your course teaches you to use tables for layout, ask then why the W3C says tables are not for layout and why professionals use divs and css (not inline styles applied from the toolbar) to control things. Also ask the teacher which doctypes you should use to avoid triggering quirks mode. If they can't answer immediately, they don't know what they are doing.