Each page can be changed to a different column layout. Just place the cursor on that page and change the layout. It only changes that page. When new pages are created by typing or using a page break they have the same layout as the preceding page. That's why it looks like you are applying it to the whole document. Just create the layout you want on the first page, and change it as desired as you create the new pages
For long complicated documents that you don't want to adjust constantly, Tim's suggestion of write it all then change the layout is probably best.
You can also place columns almost any way you want on a page by using the Text Shape. Just create the shape, copy paste the text inside it, then resize and adjust it until all the text is visible where you want it. This should work pretty well with short articles that take up no more than one page. Get rid of the boarder (if you want) by changing the shape's style.
For page breaks, with the ruler tools visible tap on the tab icon (arrow pointing at a vertical line). You can create tabs, line breaks, column breaks, and page breaks. To remove them (I don't know of any way to make them visible) you place the cursor after them and tap delete until the break collapses to the previous page/column/line.