You can select the active tool from the Toolbar dialog. If you accidentally close the window, you can show it again by checking View | Toolbar.
This tool, as its name suggests, can be used to select rectangular areas of the image. To move/resize the selected area, use the Transform (F) tool.
You can select elliptical areas with this tool.
The lasso is a tool for selecting freehand areas.
The wand can be used to select areas of the same color. Click on the canvas to select the neighboring pixels which are similar in color. Use the Tool Behavior dialog to configure the color tolerance of the wand.
Draw as if you drew with a pencil to select the pixels.
This tool can be used to transform selected areas. A special mouse cursor indicates if nothing is selected. You can resize the selection by grabbing its sides or corners, or move it by dragging every other pixel of the canvas. If you hold down Shift while dragging, the selection will drag a stripe wherever it moves. Hold down Ctrl when starting to transform the selection to keep its copy at the initial place.
Select a part of the image to keep it discarding all other pixels. Hold down Shift to select a square.
You can use this tool to set the so-called hot spot when working on a cursor. The hot spot is a pixel of the cursor with which you click on objects. For instance, considering an arrow-shaped cursor, the hot spot is the end of the arrow. Click and drag to place the hot spot to another place on the canvas. The hot spot is indicated with a red X.
The eyedropper is used for picking colors from the canvas. Click with the left button to pick the foreground and with the right button to pick the background color. If the Eyedropper switches back checkbox is checked in the Tool Behavior dialog, the eyedropper will switch back to the previously selected tool after finishing its work.
This tool can be used to perform various tricks on the image, especially on photos. The Retouch tool works as a brush and can be configured in the Tool Behavior dialog box. It can work in Blur, Sharpen, Dodge (lighten), Burn (darken), Hue and Sponge modes.
Click and drag on the image to draw a rectangle. Hold down Shift to draw a square. Use the Tool Behavior dialog for configuring filledness and line width.
Click and drag on the image to draw an ellipse. Hold down Shift to draw a circle. Use the Tool Behavior dialog for configuring filledness and line width.
Click and drag on the image to draw a straight line segment. Hold down Shift to draw a line in a special direction. Use the Tool Behavior dialog for configuring line width.
Click on the canvas to open a dialog box where you can type the text and adjust font settings. After clicking OK, the text will be inserted as a floating selection.
This tool can be used to draw a freehand, 1-pixel-wide line on the canvas.
This tool can be used to draw a freehand line on the canvas. Use the Tool Behavior dialog for configuring brush shape and width.
The eraser is similar to the brush. In effect, it helps you paint with the transparent color. Use the Tool Behavior dialog for configuring brush shape and width.
This tool is in fact a brush which paints with the foreground color only on areas of the background color (reversed if you press the right mouse button). Use the Tool Behavior dialog for configuring brush shape, brush width and color tolerance.
Click on the canvas to fill one-color areas of the image. (You can drag the mouse while holding down the left button to preview the result of the operation.) Use the Tool Behavior dialog for adjusting color tolerance.
Click and drag on the canvas to draw a gradient between the foreground and background colors. You can use the Tool Behavior dialog for adjusting gradient and repetition kind.