GNU Image Manipulation Program (GIMP) is a free package that can be used to edit images on a professional level. In many ways, it is similar to photoshop. There are many features beyond what is included in this introduction, and online tutorials are easily accessible.
Download GIMP by going to https://www.gimp.org/downloads/ and choosing the version for the operating system that you’re using. It is a fairly small file, so you shouldn’t have much difficulty running it.
Layers are the main mechanism for using GIMP. Changes you make will usually be saved on different layers, which you can move around, delete or alter. To make a new layer, just click the “New Layer” button in the Layers dock or go to the top toolbar, go to Layer and click New Layer. As you work with images, you can play around with the layers to make interesting effects, such as changing the opacity and moving part of an image to a different layer in order to make selective changes. Clicking the eye button next to a layer toggles whether or not you can see.
To import images, just drag them into GIMP. If you’re having difficulties, make sure that you’re using the original file of an image, not one being displayed in a different application. Make sure that you move around layers as you import images in order to have the images visible in the way you want.
Depending on your objectives, there are many different ways to edit and alter your images. Video and text tutorials for the advanced features are common, and the simplest ones are mostly self-explanatory. For example, to create a rectangle you click the rectangle drawing icon in the toolbar and drag until it is the size and position that you want. In the interests of not making this introduction overly complex, it will stick to the general mechanics of GIMP that you may have trouble with.
If you’re planning on printing an image, you’ll want to scale it. Once you have the finished image (when possible avoid scaling until after you’re done), go to the top toolbar and click image. From there, go to scale image. If you know the pixel size you want, just change the numbers. If you leave the lock on, it will automatically resize the dimension that you don’t alter to not create weird distortions. If you’re printing, you’ll probably want to change it to centimetres. Click the pixel button next to the size to open a drop down menu, and choose your preferred units. Once you’ve made these changes, the image will print in the size you chose.
Once you’ve finished working with an image, don’t just click save. Save keeps it as a file for GIMP to use. Instead, go to File and choose export. There are lots of options, but the two ones that you’ll probably want are JPEG or PNG. If your image involves transparency in some way (say, a non rectangular logo), choose PNG. Otherwise choose JPEG. Saving as either of these files allows you to easily share and use the image that you’ve created.