You can use drag and drop to move the positions in which pages, categories, products etc appear.
Pages
On pages, you click and drag the page into its new position and it is instantly changed on your website and in your navigation.
Products
In Product Manager, when you hover over the product you can use drag and drop to change positions. Again, this is instantly live as soon as it is dropped.
On products, you have to untick the box "Uncheck here to be able to reorder products", it's a little safeguard we put in place to stop accidental reordering of products.
Where you have categories and/or products, click on the Show All link to list all of the products before you re-order them. Otherwise if you re-order from within a category with multiple pages it will throw out the overall sort.