MeshBaker Documentation
The "Combiner" classes (MB3_TextureCombiner, MB3_MeshCombiner, MB3_MultiMeshCombiner) are ordinary C Sharp classes that do NOT inherit from Monobehavior. They can be instantiated using the new operator. These contain the core baking functionality.

The "Baker" Clases (MB3_TextureBaker, MB3_MeshBaker, MB3_MultiMeshBaker) are Components. Their state is serialized when a scene is saved. they can be found using GetGomponent or FindObjectOfType, they receive events and can be used through the inspector. They have a similar API to the corresponding Combiner classes. Internally they are wrappers that use the Combiner classes.

The "MB_TextureBakeResult" class stores the result of a material baking operation. It contains a list of materials that were combined and the corresponding UV rectangles in the atlases. It is needed as an input in the mesh baking. It is a ScriptableObject, so it can be saved as an asset in the project. You can also select it in the project and view its contents in the inspector.