Once you have downloaded and unzipped the file, pick which polaroid you want to use and save it into your pictures. Open it up in your photo editing software, I am using gimp because I am cheap and do not have photoshop :)
This layer will be your background so go ahead and label it as 'background' just to keep things organized! Now duplicate the background layer by going to layer > duplicate layer. Another layer will now show on the side bar and go ahead and name that as 'layer 1'.
Using the rectangular marquee tool, draw a square around the black portion until the lines start snaking around the box. With the black portion still drawn around, add a layer mask by going to layer > mask > add layer mask.
Now export this file and save it as polaroidclippingmask.jpg or whatever image type you like to work with. This will be your template for all the images you make.
To insert a picture, go to file > open as layers. The image will come up very small, but to not fret my friends, we will resize it to fit! Click on the scale tool then click on the image you just opened and drag the image to fit into the black box.
Once you are satisfied with where you have it, click scale. Create a layer mask again by going to layer > mask > add layer mask.
Once you have the image correctly inside the polaroid you can flatten the layers by going to image>flatten image. This just combines the layers so you don't have to worry about them moving on you!
Repeat this with 4 different images!
Now, to make things easier and to save photo paper, open a new page and make it US letter size, 8.5x11. Open up all 4 images you created. One at a time, copy a picture then go to edit > paste as > new layer
The image will come up really big but click on the scale tool and rescale it! I rescaled it down to
4.3 x 5.70 but it is entirely up to you!!