You place the cursor in a corner of the area you are going to trim out and hold down the left mouse button and drag the cross hair across, up or down, over the area you want to trim. When you have done that let off the mouse button and a square or rectangular outline will appear. You can further adjust the size of the area by clicking on one of the squares in each corner and moving it up, down or across to increase or decrease the size of the outlined area. If you do not like the results place the cursor outside of the outline so it looks like a circle with a slash in it and click the left mouse button and the outline disappears and you can try again. If you do like the results place the cursor inside of the outlined area and you will see the letters OK. Click the left mouse button and the area outside of the outline will be cropped out. If you still do not like the results click on the UNDO button and try again.