These tools are fairly easy to use. You simply select them and start drawing on the canvas. Watch the drawing tutorial or follow along below...
The first drawing tool is the pencil . Simply click on the pencil and start drawing on the cavas. To change the size and other features, then look at the properties box below the tool.
You can change the opacity, the mode, the brush size and style, you can use color from gradient, etc. The pressure sensitivity is for when you are using a drawing tablet (Wacom is a good one).
The next one (first in the 4th row) is the paint brush . It works essentially like the pencil, just more smooth. Make sure you play around with the properties and use different brushes for different effects.
The next one is the erase tool . It will erase to whatever color the background color is. Good for touching up things.
After the erase tool is the Air Brush tool . This tool emulates the effects of an airbrush.
Next up is the ink tool . This tool has some different properties so try those out. It acts very similar to a real ink pen.
The next tool is the clone tool . To clone, select this tool, then if you have an area you want to duplicate, then hold the 'ctrl' key and left click the mouse where the area you want to duplicate is. Then move to another area and hold down the left mouse key and start drawing. It will replicate whatever area you 'ctrl'd clicked.
You can also clone patterns as well. Just choose pattern source from the properties.
To blur or sharpen an image use the blue/sharpen tool . This tool comes in handy when you want to pop something out and create more of a foreground / background and to add some depth. Make sure you have the correct setting chosen from the properties box.
The smudge tool is next. This tool does just that, adds smudges. Click and drag to add a smudge. Good for blending.
The last tool in the GIMP menu is the burn / dodge tool . If you set it to burn it will darken an area, it you set it dodge it will lighten an area.
Ok, that's it for the basics. Next up we'll cover how to design your image using layers to make editing and applying effects a lot easier...
. Simply click on the pencil and start drawing on the cavas. To change the size and other features, then look at the properties box below the tool.
. It works essentially like the pencil, just more smooth. Make sure you play around with the properties and use different brushes for different effects. 
. It will erase to whatever color the background color is. Good for touching up things. 
. This tool emulates the effects of an airbrush. 
. This tool has some different properties so try those out. It acts very similar to a real ink pen.
. To clone, select this tool, then if you have an area you want to duplicate, then hold the 'ctrl' key and left click the mouse where the area you want to duplicate is. Then move to another area and hold down the left mouse key and start drawing. It will replicate whatever area you 'ctrl'd clicked. 
. This tool comes in handy when you want to pop something out and create more of a foreground / background and to add some depth. Make sure you have the correct setting chosen from the properties box.
is next. This tool does just that, adds smudges. Click and drag to add a smudge. Good for blending.
. If you set it to burn it will darken an area, it you set it dodge it will lighten an area.