Add a border/frame to a picture and provide detailed step by step instructions on how to do it

I have a set of images/pictures which were created for me in Adobe Illustrator. I'd like to upload them to a few sites for retail sale as prints, but I first need to add a shadow like border to frame them. I have attached an example of the style of frame I would like to use. I need someone to add this shadow frame to one of my pictures using Photoshop and then give me written step by step instructions on how to add the same frame to the rest of my pictures. I have Photoshop CS6 so the instructions would have to be written for this version. I would also like instructions on how to save the pictures in different sizes as I'm not sure what size/s the retail sites will require. I am a complete beginner to Photoshop, so the instructions will need to be very detailed and preferably include screen shots as I'm not familiar with the names of all the tools, shortcuts, menus etc.