There's no one answer to that since different models are.. different. Beyond just modalities (text input and image output? image input and video output?), there are different common underlying tools used to build them. And then, of course, what do you mean by API? How do you want to interact with it?
As a general thing, you'd take a request that would require an inference step, which would then invoke the model with some parameters and input, and return the output. Beyond that, you'd need more detail.
As a general thing, you'd take a request that would require an inference step, which would then invoke the model with some parameters and input, and return the output. Beyond that, you'd need more detail.