Insert Parts and Assemblies inserts instances of parts, assemblies, sketches, and surfaces into the active Assembly. You can instance specific parts (released or unreleased), sketches and surfaces defined in a Part Studio (or the entire Part Studio), and assemblies defined in a different Assembly tab, as well as all of these things from other documents (linking documents). Filters for each object type are available in the dialog when the corresponding entities exist in the current document or other documents being browsed.