One of the most important processes for any Photoshop user from beginner to professional to understand is making selections. Selecting a specific part of a photo is essential to photo editing. Like any other process in Photoshop, there is more than one way to go about it.
If you look in the top left of the toolbar, you will find the marquee select tool just adjacent to the move tool. This tool defaults to rectangular marquee. This is the simplest and most intuitive of all selection tools, but is not without its limitations. With this tool selected, you simply click and drag to make square/rectangular selections of any proportion.
By clicking and holding the left mouse button on the marquee tool, a side panel drop-down menu will give you a choice of three other versions of the tool. These are: the elliptical tool, which allows you to make circular and oval selections, the vertical marquee tool, and the horizontal marquee tool. The latter two of these are not particularly useful.
On the toolbar, just below the marquee tool, you will find the lasso tool. This tool is only slightly more complex than the marquee tool, but much more powerful. By clicking and dragging, you can use the lasso tool to make a selection in any shape whatsoever. Releasing the left mouse button will make the selection active.
Just as with the marquee tool, you can bring up a drop-down menu by holding down the left mouse button on the lasso tool, bringing up two other types of lassos. The polygonal lasso works slightly different than the standard lasso but can be used to select complex shapes. By clicking, you set the start point. Each time you wish to draw at another angle, you click again. The selection is complete when you click at the start point, closing the selection. The next lasso tool is the magnetic lasso. This is the most useful tool for extracting specific elements of a photograph. The magnetic lasso automatically follows the contours of an object by the differences in light and dark. The sensitivity of the magnetic lasso is determined by the percentage of the edge contrast, located in the action bar at the top. Just like the polygonal lasso, you have to click back on the start point to close the selection.
The last of the selection tools is the magic wand which is located just to the right of the lasso tool. The magic wand makes selections according to similarities in color and saturation. If you click on a photo with magic wand, you will notice that it automatically selects a patchy group of color. By holding down the shift key, you can add more to the selection by continuing to click. Lowering the tolerance level in the action bar restricts the variance in color and contrast that the magic wand selects.
That's pretty much it. One last trick though: right clicking after making a selection will give you some extra options like: inversing the selection or feathering the selection (softening the edges).