Summarize the following:
If you just want to create a simple collage with different transparencies, you can use an online tool to do so without having to download and install GIMP. You can't use Pine Tools to introduce a new photo, such as a celebrity, to a base photo in hopes of convincing people that the end result is a real photo. This is helpful when selecting photos to add to your project as layers. You may want to make a copy of the photos you plan on using by selecting them, pressing Ctrl+C (Windows) or ⌘ Command+C (Mac), and then pasting them in a common location such as the desktop. Once you know which photo you want to use as the background for your final image, you'll need to find the width and height (in pixels) for the photo so that you can create a properly sized canvas later:   Windows — Right-click the photo, click Properties, click the Details tab, and look for the numbers to the right of the "Dimensions" heading (you may need to scroll down).  Mac — Click the photo to select it, click File, click Get Info, and review the "Dimensions" heading in the "More Info" section (you may first have to click the More Info heading). Do the following depending on your operating system:   Windows — Go to https://www.gimp.org/downloads/, click Download GIMP directly, double-click the downloaded setup file, and follow the on-screen instructions.  Mac — Go to https://download.gimp.org/mirror/pub/gimp/v2.8/osx/ in your computer's web browser, click the gimp-2.8.10-dmg-1.dmg link, double-click the DMG file, click and drag the GIMP logo onto the "Applications" folder, and follow any additional instructions. On a Mac, you may need to verify the installation before you can install GIMP. Once you've installed GIMP, you can proceed with opening it, after which point you'll be able to begin overlaying your photos:   Windows — Click Start {"smallUrl":"https:\/\/www.wikihow.com\/images\/0\/07\/Windowsstart.png","bigUrl":"\/images\/thumb\/0\/07\/Windowsstart.png\/30px-Windowsstart.png","smallWidth":460,"smallHeight":460,"bigWidth":"30","bigHeight":"30","licensing":"<div class=\"mw-parser-output\"><p>I edited this screenshot of a Windows icon.\n<\/p><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"http:\/\/en.wikipedia.org\/wiki\/Public_domain\">Public Domain<\/a><br>\n<\/p><\/div>"}, type in gimp and click GIMP at the top of the menu.  Mac — Click Spotlight {"smallUrl":"https:\/\/www.wikihow.com\/images\/e\/ea\/Macspotlight.png","bigUrl":"\/images\/thumb\/e\/ea\/Macspotlight.png\/30px-Macspotlight.png","smallWidth":460,"smallHeight":460,"bigWidth":"30","bigHeight":"30","licensing":"<div class=\"mw-parser-output\"><p>I edited this screenshot of a Mac icon.\n<\/p><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"http:\/\/en.wikipedia.org\/wiki\/Fair_use\">Fair Use<\/a><br>\n<\/p><\/div>"}, type in gimp, double-click GIMP, and click Open if prompted.

Summary:
Consider using PineTools. Make sure all your photos are in one location. Find out the size of your main photo. Download and install GIMP. Open GIMP.