The status bar contains help, progress, and information that is very useful while working in Paint.NET.
Whenever you select a tool, this section of the toolbar will contain some quick help text that summarizes how to use the tool. Some tools, such as the Line / Curve Tool, will change the displayed help text depending on what actions you have already performed. Many tools will also use this area to display information about what you are currently doing, such as the size or length of a selection or shape.
When you use an Effect or an Adjustment, its progress towards rendering completion will be displayed here.
This displays the current size of the image. It will display the dimensions of the image in pixels, inches, or centimeters, depending on what you have chosen in the View Menu or the Toolbar.
This will display the current cursor location in document-relative coordinates. It will display these in units of pixels, inches, or centimeters, depending on what you have chosen in the View Menu or the Toolbar.