Build Assembly Rig
Build Assembly Rig is the automatic rigging step inside the Assembly Resource. From the parts' pivots it works out which part attaches to which, and builds the rig that lets an Assembly Decoration bend the parts with effectors and wind while they stay instances. It is hidden from the Tab menu; use the Assembly Resource, which runs it for you.
Rigging relies on each part's pivot sitting at its base, where it joins its parent. When the pivots are elsewhere, parts attach to the wrong neighbour or not at all; fix them with Pivot Edit, or the Edit Pivot state on the Assembly Resource.
Settings
The Search settings control how the node looks for each part's parent, and the defaults suit most kits. Under Output, Assembly Name is the attribute that names each assembly (assembly_name), and Prefix starts each assembly's name (assembly). Lost Parts sets what happens to parts it can't attach: mark, remove (the default, and recommended) or ignore. Group, under Inputs, picks which parts are rigged, by default every part except atoms. Under Advanced, Cluster Attribute (cluster) reads the grouping that Partition Assemblies writes before this step in the Assembly Resource.
Bake
Bake projects detail from high-poly geometry onto a low-poly mesh's UVs and writes colour, height and normal maps, for scanned trunks and tiling textures.
Classify
Classify places the parts of an assembly library on a two-trait chart, as its own step on the assembly wire. It is the same chart the Assembly Decoration and Clusters Decoration have inside.