You cannot insert a page break in a section, only before or after... Here's how:
Once you have assigned levels of grouping to the report, and made a header and/or a footer visible for these groups you can click on the properties of said header/footer and under the Format tab you will see the item;
Force New Page
You can elect to select either:
Before & After Section
I've just tried it and you can use the "Page Break" control to insert a break anywhere you need to, whether it's a section or summary/footer etc. The Page Break control is shown in the Toolbox of the report design screen and looks like two split pages with an arrow pointing to the break (on my screen it's between the "Bound Object Frame" button and the "Tab Control" icons.