Selection

PHOTOSHOP

Marquee Tool is used to select areas of standard geometric shapes like reactangle and oval
Choose the Marquee Tool. Click and drag over the graphic area that you want to select
To deselect the selected area, press Ctrl + D
Lasso Tool is used to select areas of irregular shapes
Choose the appropriate Lasso tool and use freehand trace to outline the area of selection
Magic wand Tool is used to select a particular color

The Tolerance Level is adjusted. The Lower the value the smaller area is selected

Marquee Tool, Lasso Tool and Magic Wand Tool will all have the selection refining bar in their options
New Selection is used when you first draw a selection
Add to selection is used when you want a newly added selection to join up with the old selected part
Substract from selection is used when you want the newly drawn selection to be deleted from the drawn selection
Intersect with selection is used when you want the common region between the old and the new selection to be selected

For Marquee and Lasso Tool you will have a feather option in their Options Toolbar
Choose a feather eg. 20
Use the Marquee or Lasso Tool to Draw a selection
Right Click > Layer via Cut
You Layer Panel will now have 2 layers
Delete the bottom layer ( the layer with the part of the picture you do not want)
Add a new layer and plce it below the feathered section. Fill it with a color or gradient