Open a blank, new file from the File menu (File>New>blank file). Enter the width & height of your paper stock, resolution 300 px/in, background white, or any other color. This will be your canvas. Ideally, the resolution should be the same value as that of your 3 pictures.
Open picture #1, and with one of the selection tools, e.g. selection brush, lasso tool, select the object that you want
Go to Edit menu>copy to place it on the clipboard
Go back to the canvas
Go to Edit>paste, and the object will be on its own layer.
Use the move tool to position the object, and to resize with the corner handles of the bounding box