By default, the sort order for queries in WordPress is descending. This will produce posts in reverse chronological order, the desired result for most blogs.
In some cases, it may be desirable to have posts in ascending order. When activated, this plugin changes the default order from descending to ascending. This affects all queries (home page, archives, dates, etc). Deactivating the plugin returns the default order to descending.
IF YOU DON’T LIKE THE RESULT, IT’S THE THEME
How well this works out varies from theme to theme. Depending on a theme’s navigation labels for posts, things may or may not make sense. If labels are “Earlier” and “Later”, things will seem backwards. Some themes make sense either way. For example, in the “Twenty Fifteen” theme, “Previous” is above “Next”, suggesting list order rather than time.