Lasso ToolThis is a freehand selection tool. Click and hold your left mouse button on the image and draw your selection.
Polygonal Lasso ToolSimilar to the lasso tool, except that instead of holding your mouse button down to draw, left-click on various points to create a selection with a series of straight edges.
You can also hold down the Alt key (Windows) or Option key (Mac OS) to draw freehand sections.
Magnetic Lasso ToolThis is a very handy tool for selecting areas which have reasonably well-defined edges. Left-click at the starting point of your selection and simply move the mouse along the edge.
"Fastening points" are automatically made at various points along the edges. Left-click at any time to add a fastening point manually.