Step 1. Open a new file. You can do this by hitting ctrl+n. I made my image 710x600 pixels, which is about the width of my post area.
Step 2. Find a product you'd like to feature in your collage. The first product I chose was from this shop. Be sure when you choose a photo, it should be a simple shape and easy to cut out. It works best if it's on a plain white background, too. Once you have your product, copy a photo of it and paste it into Photoshop.
Step 3. Zoom in a bit (magnifying glass icon) and take the eraser tool (pink eraser icon) and erase most of the background surrounding the item. Leave space for the smaller and detailed erasing.
Step 4. For more careful and precise erasing, I use the paintbrush tool. Set your main color to white then click on the little paintbrush icon near the top of the screen. This will pull up an options bar. Set the hardness to around 40% and then you can paint over the background slowly and carefully.
Step 5. Zoom back out and check your work. If it's still rough around the edges, you can zoom back in and clean it up.
Step 6. Once you've repeated steps 2-5, place your different images evenly. You can add a title to it, too.