It automatically arranges your load order. Read the page it brings up because it may have warnings about certain mods, such as not compatible with X or make sure you only have one of it's esp files (for mods that have multiple esp files but only one is needed).
It will take all esp files that it does not recognize and place them at the end. If you use Wrye Bash and use a Bashed Patch then place those mode before the patch unless in their readme it specifically says to load them after that patch (very few mods do that).