There are two main ways that different AI models use seeds.
Model generates seed value:
Stable Diffusion
Bria
Stable Diffusion 3
Adobe Firefly
In this case, each image generated by the model comes with a seed number generated. You can find out more about how to locate and use seeds in this way in this article
User generates seed value:
Imagen
Getty Images
Runway (video)
Veo2 (video)
Stable video (video)
In this case the model will never generate a seed value for you. If you want to make use of seeds, you will need to populate the ‘Seed’ box for a generated image or video that you like. You can then populate this same value into future generations to make use of the seed.
A guide to using seeds in Image Generation can be found here