Rectangle Select
This tool is used to define a rectangle or square selection region
Move Selected Pixels
This is used to move pixels that are selected
Lasso Select
This is used to draw a freeform selection region
Move Selection
Used to move the selection without affecting the pixels that are selected
Ellipse Select
Used to draw an ellipse or circle selection region
Zoom
This tool can be used to zoom in (left click), zoom out (right click), or zoom the whole canvas around a particular region (draw a rectangle).
Magic Wand This tool is used to select areas of the active layer that are similar in colour.
Pan Tool
Paint Bucket
This tool is useful for filling in areas of similar color with a different colour.
Gradient
Paintbrush
This tool is selected by default when you start Paint.NET, and is useful for many kinds of freeform drawing.
Eraser
You may use this tool to erase areas of the image (it sets the transparency to 0).
Pencil
This tool allows you to edit the active layer pixel-by-pixel.
Colour Picker
You can use this tool to pick up a color from the active layer and set it as the current primary or secondary color.
Clone Stamp
This tool is useful for copying regions of pixels between layers, or within the same layer.
Recolour
This tool is useful for replacing one color with another.
Text
This tool is used for placing text on the image.
Line/Curve
This tool is used to draw straight and curved lines.
Rectangle
This tool is used to draw rectangles and squares.
Rounded Rectangle
This is used to draw rounded rectangles and rounded squares.
Ellipse
This tool is used to draw ellipses and circles.
Freeform Shape
This tool is used to draw a shape with a freeform outline.