A multicolumn latout is typical of a newspaper article. You start reading down the first column and then when you get to the bottom, you start again at the very top of the next column. Of course it all depends on how tall your window is. And how is that controlled? By the width of the columns. Netscape will try to divide the text evenly among the columns you've defined, making them as long as necessary, but as even as possible.
Use page breaks wherever necessary to start a new line. Or, use a line break instead. Or insert images, whatever!
After the MULTICOL tag, you can go back to creating one column text. Or you can create another set of columns, with as many columns as you like.