From top to bottom:
1) The white
arrow allows you to select a particular image if you have multiple
images open.
2) The magnifying glass zooms in on left click
and zooms out on right click.
3) The deformation button allows
you to deform a selected area (see below) of your image. It is useful for
creating perspective renderings.
4) The crop button allows
you to chop to a selected portion of your image.
5) The layer
movement button allows you to move a layer to a new position.
6)
The selection button allows you to choose a portion of your current
image.
7) The lasso button allows you to freehand select a
portion of your current image.
8) The wand tool allows you to
select a portion of your image that matches predefined color criteria.
9) The eye dropper button allows to precisely select a color
from an area of your current image.
10) The paintbrush button
allows you to draw a line at a width that you define.
11) The clone
brush allows you to select the small portion of your image and paste
over another area in your image.
12) The color replacer button
allows you to replace selected colors in your image.
13) The retouch
button allows you to change the appearance of portions of your
image.
14) The eraser tool allows you to erase a portion of your
image. Note: the eraser color is set with the background color
selector.
15) The picturetube button allows you to add theme
imagery to your image.
16) The spray can allows you to spray
paint a color and/or texture onto the current image.
17) The
paint bucket allows you to fill a closed portion of your image with
a color and/or texture.
18) The text button allows you to add
non-editable text to your image.
19) The line button allows you
to create a variety of line types.
20) The shape button allows
you to create a variety of shapes.