A typical assembly file is composed of links to the included components and assembly constraints. The components are parts or subassemblies that exist as separate files. When these components are placed into an assembly file, links to those individual files are created in the assembly file. Initially a component is free floating and can be moved and rotated in any direction, unless grounded in place or constrained to other components.
For example, if you were to create an assembly of a simple drilled base plate and a bolt to be inserted in the hole you would have three files:
The assembly file (
The base plate part file (
The bolt part file (
When the part files are placed into the assembly file, ...