Kraut is a tool for procedurally generating trees and other plants. Tree files are authored in the stand-alone Kraut editor, which you can get here.
The Kraut asset references the .tree file that the Kraut editor writes. You then have to specify the materials that shall be used for each tree part. Note that there are three Kraut specific base materials (under Plugins/Kraut) which have to be used as the base materials. Kraut uses a custom shader, and these base materials pull in the correct shader and configure it to be used for stems (trunk, branches, twigs), fronds (static leaves) or leaves (billboards).
Once a Kraut tree config is imported and set up, dragging the asset into a scene, will instantiate a Kraut tree component.