Use the Mod Filters to search for craft according to the mods that they use. Select 1 or more mods using the mod search text field and KerbalX will find craft that use those mods. The filters can work in three different ways;
This filter will find craft that will work if you had the selected mods installed. The craft returned will use all or a subset of the selected mods.
For example if you select "B9" and "BahamutoD's Armory", the craft shown will either use just B9 or just BahamutoD's Armory or both together.
This filter finds craft that use all of the selected mods and may also use other mods.
For example if you select B9 it will find craft that have atleast 1 B9 part (amongst others). If you then selected KAS it will find craft that have at least 1 B9 and 1 KAS part.
This filter finds craft that use all of the selected mods without any other mods.
Like include, it will find craft with at least 1 part from each selected mod, but unlike include they won't have parts from any other mods.