prompts: An astronaut riding a horse in photorealistic style.
If you want an easy to use solution, I will recommend Midjourney. It no doubt produces the best results, especially for none professional users. Unlike Stable Diffusion and DALL·E 2, you can't install Midjourney on your own computer or use a nicely designed web app. The only way to access it is through Discord. You can see others results and learn a lot through others using Midjourney in Discord.
Here's the short list of how to use Midjourney:
Sign up for Discord.
Sign up for Midjourney, and accept the invitation to the Midjourney Discord channel.
Go to a #newbies channel, and type /subscribe.
Pick your Midjourney plan.
Head back to Discord, and start generating images.
Edit, upscale, and download your creations.