Eyedropper Tool is used to choose the exact color as in an image. A Color Picker tool is an application used for the purposes of exracting color from an image.
Video Tutorial:
Eyedropper Tool:
The above video teaches you how to use the eye dropper tool.
Choose the "Eyedropper" or also color picker Tool from the "Tool Bar".
Click on the portion of the image whose color is required.
The color chosen by this tool is displayed in the fill color box.
The same color gets displayed in the properties window of the "Eye Dropper" tool also.