How to use the multilateral lasso tool to map into two

If the title
with PHOTOSHOP

noose with which to select and then cut acridine part of the constituency to choose shear, Create a new document and then paste to save a file

to return to the old paper cutting tool to choose a good size, and then save the file as if the two just want to map will be split into two, I think rectangular box with a more convenient point.To Do not select a place like the press Delete.But if it is to map the interception of a certain part of the characters and the like, for example, use magnetic lasso more accessible and user-friendly, remember that the points raised frequency.