The Lasso tools work in a way very similar to the Marquee Tool, the difference being that the Lasso tool allows you to select free-form shapes.
The Tool 
When you enter into the higher level photoshopping techniques you will often need a more detailed selection edge. For these situations the Lasso tool is better suited for performing selections. First, click on the Lasso tool and scroll over your canvas. Then click and hold the mouse, and trace the area that you wish to select. That area will become selected when you let go of the mouse. In almost all ways other than shape the Lasso tool is identical to the Marquee tool. Variations include the Polygonal Lasso tool, which you use by selecting points and the area between these points will make up the selection edge, and the Magnetic Lasso tool, which is a sort of "AI" assisted Lasso tool.