Lasso Tool
Lasso tool is also a selection tool. With lasso tool we can select extremely typical or complex areas of an image. Lasso tool selects objects by drawing either a freehand or straight-edged selection area. 
Select object by lasso tool
(i) Choose "Lasso Tool" from the tool bar.
(ii) Click and draw a free form line around the object being selected. You must end at the starting point.
Free form line around the object.
Selected object
Selection by polygon lasso 
Original object
(i) Click "lasso tool". 
(ii) Click "polygon modifier " from the option tray.

(iii) Click point 1,2,3,4 and 5 to draw a polygon around the portion to be selected.

(iv) Double click starting point (point 1)when finished selection.
Segment is selected
You can separate selected segment . 
You can change any thing of the selected segment.