Click once on the edge of the feature you want to select. Then carefully draw around the edge of the whole feature. You will find that the selection will be drawn 'magnetically' to the edge, correcting any small mistakes you may make. Double click to finish the selection.
As you draw you will see Photoshop setting 'fastening points'. If Photoshop seems to be having trouble detecting an edge you can help it by clicking to set a fastening point manually. On the other hand, if it has set a point in the wrong place you can undo the last point set by hitting backspace,
Width - sets the width of the 'brush' you are using, i.e. the amount by which you can stray away from the edge.
Edge Contrast - low values allows Photoshop to detect edges which differ only a little from their surroundings. High values will detect only high contrast edges.
Anti-aliasing and feathering - nornally switch anti-aliasing on and set feathering to about 3 pixels.
New selection, add to and subtract from can be set with the options at the top of the screen (just to the left of the 'feathering' box. Alternatively, you can hold the Shift or Alt key down while selecting.
After making a selection it is worth zooming in to check that there are no minor errors. You will often find that a little bit of sky has been selected in a corner, or that the tip of a flower petal has been missed. While it may not seem important now it will stand out like a sore thumb later (especially if you cut and paste). Correct these by adding to or subtracting from the selection with any suitable tool.
The magic wand can be used to select on the basis of colour.
Use it to click anywhere on an image. You will see that all the surrounding area that is of a similar colour will be selected.
Click somewhere else to add to the selection all parts of a (slightly) different colour.
Tolerance - low values selects only those colours which are very close to the selected point. High values selects colours which differ more.
Contiguous - if on, only selects areas which are contiguous with the selected point. If off, selects areas anywhere on the picture which are of similar colour.
You will often find that few pixels in the middle of an area have not been selected. The easiest way to include these is to 'round them up' with the lasso tool.
Using this you can 'paint' the area you wish to select.
Brush roughly within the area you want selected. When you release the mouse button Photoshop will attempt to guess what you wanted. Sometimes it gets it right.