Layering begins once the image is stored on your computer, the image will usually open itself in the default programme so you will have to open Photoshop and then find the image you want to open using file – open – and then where the image is stored.
This is when you will do all your manipulation, layering and resizing using Photoshop itself. Once you have completed this you will then save your changes, if you save the images straight into Photoshop it will save them as a PSD, PDD or EPS file. If your image is saved in these particular formats your file will stay large and hold the quality whilst preserving all layers, this is the best file format to use if you are going to be reworking the image.
Other choices of formats for your file are TIFF – which will keep the quality but are large files and best used in design for print, BMP or bitmap is a windows file that creates good photos but creates large files and a PDF is a adobe acrobat file which locks texts and images so they cannot be further manipulated, usually used as a file for sending information or important documents.