Prior to reading this tutorial it would be advisable to have read the Marquee Tool tutorial first to understand basic selections.

The Lasso Tools allow for more manual selection methods.  They allow more refinement than the Marquee Tools.  To access the Lasso Tools either click on the icon and hold to access the submenu, or cycle your choices by using the shortcut key on your keyboard, which is L.  Your three options are the Lasso Tool, the Polygonal Lasso Tool and the Magnetic Lasso Tool.  Each is used in different ways to select areas of an image to edit, delete or copy and paste as required.

Let's start with the main Lasso Tool, and a stock image of a woman sitting at her laptop:

With the Lasso Tool we can create a vague outline of the woman and her laptop.  the image would need more refinement but it's a start. To use the Lasso Tool, just click and start drawing around the selection you want to make.  Don't release your drawing until you loop back to the beginning.  See my selection below:

As you can see this is a very quick way to make a rough selection around a more complicated shape.  We can then do as we please with the selection as per the methods in the Marquee Tool tutorial.  In this case though let's just copy and paste into a new image.

Now if we jump to the Magnetic Lasso Tool we can start to refine the more contrasted areas of our pasted image.  The black background layer is there for visible contrast, but we will be working on our pasted layer.  The Magnetic Lasso Tool tries to stick to the strongest edge it can 'see'.  The white background against the skin, hair and black top she is wearing for instance, but it would struggle with the top part of the laptop where it is white on white, or the back of the chair against the clothing which is black on dark grey.

So here I will draw using the Magnetic Lasso Tool close to the edges of the image, and see how the line creates its own control points and contours.  To use it just click once to start, once at any time to place a control point and once at the end when you loop back to the beginning:

Now that we have selected some of the clearest background we can delete it.  And if we do the same again with removing some of the desk under her arms like this:

And so we are now left with less background, but still some to remove:

To remove the rest we will use the more intricate Polygonal Lasso Tool.  This tool works by creating straight lines.  You place each control point yourself with a click of the mouse when you want a line to end.  If you zoom in on your picture you can get much more intricate and accurate.  Watch this video to see how much work can go into being as accurate as you choose. 

The video is a little over 6 minutes long and you will see that I work in small sections and delete as I go along.  The reason I do that is because if you make a mistake in a large selection then you have to undo all that you've selected so far and start again.

And here's the final clean result:

I hope that this gives you a better understanding of the three individual Lasso Tools.

Next we look at the Quick Selection Tool.