Computers, phones and tablets all have background wallpaper and great images are often bundled with the device. However, it is still fun to create your own. Use Background Generator for free.
There are two types of backgrounds for devices and wallpaper images are usually photographs and abstract designs with shapes and colors. Background Generator creates the second type and there is no end to the number of images it can create.
Background Generator is a website which works on Mac, PC and mobile, but there is also a Windows app. There aren’t any significant differences between them. It is a bit more convenient running the app if you are using a PC and there is a choice of an installer or portable version that you just unzip and run. One advantage is that it does not have the ad banner of the website.
Use Background Generator

Go to the website on a Mac or start the app on a PC and a background is displayed in the main part of the window. At the top is a collection of image styles: Colorful, Graphics, Galaxy, Changing Light, Poly, Dreamy and Bars. Select the style of image you want at the top.
An image is immediately displayed, but down below some styles is a collection of templates shown as thumbnail images and there can be up to six. It is useful to pick a template that is similar to what you want and tweak it, but you can simply experiment with the settings until you find an effect you like.

A panel on the left has all the controls for generating the background image and there are many preset sizes, including many popular computer, phone and tablet screen sizes. If you have an iPhone for example, you can simply select the iPhone model to set the size. Up to 4k screen sizes are supported and there is a custom option to make whatever image size you want.
Each of the background styles (Color, Graphics, galaxy and so on), has its own controls, so the contents of the left panel changes with the style. Some have few controls, some have a lot. The idea is that you experiment with the settings. Controls may include transparency, alpha, gradient, background color, shape color, number and size, and more.

The Changing Light style is actually an animation and you stop it at whatever point you find most visually interesting and save that frame as the background.
Background wallpaper does not usually have text, but it can be added if you want it, perhaps for branding, a company name or thought for the day. The font, style, size, position, color, alpha, shadow and other attributes can be set in the side panel.

When you are happy with the image, it can be saved as a JPG or PNG file. It is up to you to then set it as the computer desktop, phone or tablet wallpaper (just right-click/Ctrl+click an image file on a PC or Mac).
The number of images Background Generator can create must be in the millions and there are endless variations. However, you need reasonable contrast between the text captions below icons on the desktop of whatever device you need and the background, so bear this in mind.
You can always create an image, save it, set it as wallpaper, then tweak the settings and save a new version of the image.
Background Generator on a phone
Backgrounds for an iPhone or Android phone can be generated on a computer using either the website or the desktop software and then transferred to the device, but there is an even better way. Create backgrounds directly on the phone using the website.
Go to bggenerator.com and all the features of the desktop version are accessible on the phone in Chrome or Safari mobile browsers. Choose one of the background types at the top, pick a template at the bottom, tap the Options button and customize the size the settings to generate the background you want. It’s the same as on the PC or Mac.

The image is saved to the phone and you have to find it in order to use it as the background.
On an iPhone for example, open the Files app and the image is saved in iCloud Drive. Long press the file and select Share from the menu that appears. Select Save Image and it is added to the Photos library. Go to Settings > Wallpaper > Choose a New Wallpaper, tap All Photos, tap the image in the Photos library and press Set to set it as the background.
Android has different menus, but it is a similar process. On a Samsung phone for example, create the background and download it. Open the My Files app, tap Images, tap Download, tap the background image file and choose to open it with Gallery. Open the three dots menu and press Set as wallpaper.