Ollama extension assumes you already know how to run Ollama locally or know the URL for an instance of Ollama. It assumes you have already pulled models.
WARNING: Although you should know this, ollama locally takes up resources which in turn will take resources away from image generation. I suggest using small models and if you already have little V/RAM, I wouldnt use it at all.
Configurations can be found in the settings tab of Forge UI