There are many tutorials to view via Google, some good, some bad.
Clicking the
Play Video in this link shows a method of creating a -->>
compilation using three photos <<-- which in this case are layers pasted onto a background image.
It also explains how to resize and move the layers.
It's by no means a comprehensive or wide ranging use of, creation of layers tutorial, or layer effects lesson, but it's a start.
These links, amongst many others, may be a good source of information -->>
Paint .NET forums <<--
---and---
-->>
Paint.NET Overview <<-- (use the table of contents, concepts and user interface links)
Good luck and have fun.