There are three different modes for moving portlets. The first option implies replacing the target portlet with the moved one. The second variant allows portlets to be moved only along the x-axis, thus creating only columns. With the third mode, you can place portlets just along the y-axis. In this case the row structure will be built.
You can easily drag-and-drop portlets with its handler. It can be placed either as a column or as a row. What is more, a new possible position of portlet is highlighted.