Products can be arranged manually when they are displayed within their category page.

On the admin Products > Categories and select the required category by clicking on the number in the products column.

Adding a number to the position column for each product will control the order they are displayed on the category page.  We would recommend using numbers 5,10,15,etc to allow you to introduce more products into this at a later date without the need to change every product.  5,10,11,12,15,etc

You will then need to add this sorting to the list of sorting features on the store front.

In the admin Settings > Appearance and scroll down to Products list layouts settings

You can change the sorting options available to users on the category pages by the tick boxes.  You can also select the default sorting, this is a global default for all category pages.