When creating or editing an article you will see this field:
Articles are ordered by this value, with the lowest values appearing first.
By default, each article will have an ‘Order’ value of 0. That means no particular article will be shown before any other.
To manipulate the order simply edit the values to reflect the order you want the articles to be displayed in.
Negative values also work, if you set one article to ‘-1’ and the rest are the default (0). The article with the negative value will be displayed first.