First open a stored image, then click on the Marquee tool. When your cursor is over the image, it should look like a thin plus sign. The center of the plus sign (or crosshairs) is the selection point.
Click and drag the crosshairs across your image. A rectangular marquee should appear, with one corner where you started dragging and the opposite corner where you stopped. The red arrow in the picture (right) shows the movement of the cursor.
Holding down the Alt key while dragging makes the marquee open outward with the starting point as the center, rather than a corner. This is shown by the red arrow in the picture (below).
Holding down the Shift key while dragging forces the marquee to be a perfect square. Shift + Alt combines the effects of both keys and makes the square open from the center point.
After you have selected an area of the image with the Marquee tool, the cursor changes its appearance to look like a small marquee with an arrow when held over the selected area. This cursor affects only the marquee itself.
Clicking anywhere in the image will make the marquee disappear, deselecting the area. If you click and drag inside the selected area, you can move the marquee's position to select a different place on the image. You can also move the marquee by using the arrow keys.
Look at the top of the screen, directly beneath the main menu bar. You should see the Marquee menu.
First look at the area beneath the number 1 in the picture (above). This determines the properties of the selection area. The default is that you can only select one area at a time with the Marquee tool. If you try to select a second area, the first marquee will disappear, to be replaced by the second one.
If you click on the second icon in this section, which shows two overlapping squares, it allows you to select multiple areas. Each successive marquee will add its area to the previous ones. They can be either contiguous or non-contiguous.
The third icon in this section allows one area to subtract from another. After you have selected an area, click on this icon. Select another area overlapping the first, and the new selection area will be subtracted from the first. These "subtraction" areas must overlap the initial selection. If you try to select an area outside the portion surrounded by the marquee, nothing will happen.
The fourth icon selects only the junction between two selection areas. Select part of your image and then click on this icon. Select an overlapping part of the image, and only the area where the two selections overlapped will remain selected. Selecting on an area that does not overlap will give you a warning message and deselect everything.
Now look at section two, "Feather." This allows the edge of your selection area to be gradual rather than sharp. The higher the number you enter in this box, the more the edge is blurred.
The box under the number three will only be active if you use the Elliptical Marquee explained below. Anti-aliasing is a process that smooths out edges gradually. If you have a high resolution image, it is probably a good idea to leave this box checked, because the smoothness will look more pleasing. However, if you are doing low-resolution work, or if you want a cleaner, sharper edge, uncheck this box.
Section four alters the properties of the marquee. The default style, "Normal," allows you to determine the width and height of the marquee separately as you drag. If, however, you change this style to "Fixed Aspect Ratio," you can form a marquee that has the width and height set at a constant proportion. You determine this proportion by typing the ratio in the "Width" and "Height" fields in section five.
If, instead of dragging the marquee to the desired size, you wish to determine the size of the marquee by a specific width and height, change the style to "Fixed Size." You can then input the width and height that you need in the section five fields.