Exploring with Lasso Tool (L).

The lasso tool creates a custom, free-hand selection. It is usually used to cut out, or select specific sections of a pre-existing picture. Access the lasso tool by clicking on the icon located on the tool bar, or press the keyboard shortcut (L).

The Lasso Tool - L:

Extract anything from images by carefully articulating around the areas you'd like to extract. Notice this tool isn't capable of precision, there are alternative methods that are far more precise at extracting things from images.

Extract With a Lasso:

Photoshop - Lasso Tool Options

The options bar for the lasso tool holds a few options you may already be familiar with. The beginning four icons allow for the addition and subtraction of a a selection.Skipping past those icons, you find an input field allowing for the feathering of the selection as it is removed and again, an anti-aliased check box.

Lasso Tool Options Box:

Photoshop - Polygonal Lasso Tool

The polygonal lasso tool exists as a secondary tool to the original lasso tool. Press shift+L to alternate through the lasso tools until you have the polygonal lasso tool selected. This tool is great for extracting pieces of photos that have straight edges or a semi polygonal shape to them.

Polygonal Lasso Tool:

By clicking specific points around an image, Photoshop will draw straight lines from point to point as you continue to click the canvas. Use Delete - Del to undo a point and try again. This tool is not ideal for extracting complicated figures, just stick to polygons.

Select Polygonal Shapes:

Holding shift while clicking with the polygonal lasso tool creates straight lines and 45^o angles. This is a handy tip to create specific shapes like diamonds, rectangles, or triangles.
There are no new options for the polygonal lasso tool. The options box reads the same as with the original lasso tool.
This tool will lasso any polygon shape by clicking specific points around an image. Photoshop will draw in straight lines from point to point as you click around the image.

Photoshop - Magnetic Lasso Tool

Perhaps more useful, the magnetic lasso tool exists as an additional secondary tool to the lasso tool. Select this tool by pressing shift+L and toggling through until the selector rests on the magnetic lasso tool selection. This tool is unique as it identifies a contrast in an image and is draw to that contrasting point creating a selection as you briefly drag the mouse about the object of desire.

The Magnetic Lasso Tool:

This tool works best when there is a huge contrast between objects in the foreground of the photo or objects in the background. Simply click near the a high-contrast edge and the lasso tool snuggles right up against the edge as you drag the mouse cursor along the line of contrast.
How it works is, as you drag the mouse photoshop places points of selection about the image. At any time clicking along the edge will place a point. This way you can sort of help Photoshop along with the selection. Sometimes these points placed by Photoshop can get out of hand, pressing Delete - Del will undo misplaced points and you may continue dragging the mouse as Photoshop makes the selection for you.

Magnetic Selection:

This is a very handy tool but takes time to master. Use the option bar at the top of the stage to aide you in your mastery.

Magnetic Lasso Tool Options:

The first input box is title width this box allows you to change the number of pixels the magnetic lasso tool takes into account for finding contrast. Use a large pixel value for high contrast areas and a lower pixel value for tight low contrast areas. The number of pixels here can be increased or decreased using the keyboard shortcuts of ] and [ - the square bracket keys.
Next is the contrast edge amount which is a percentage that is taken into consideration as you drag the mouse cursor about the selection. Photoshop will uses this percentage to help calculate the selection. Adjust this setting if the width adjustment doesn't cut it.
The frequency box determines how often points are placed as you continue to drag the mouse cursor. An integer between 1 and 100 is required. A setting of 100 is the highest setting creating pin points faster than you can delete them.