@Marco Matascioli I am not sure if you already have a resource or trying to create one. I would suggest to first login to Azure portal and search for all your resources and locate the computer vision resource. If the resource is found you can locate the Keys & Endpoint tab and use the keys and endpoint to follow the steps of image analysis and call the API. Using all other APIs is pretty much the same where you can use the API reference to call any of them.
If you have not created any resource yet then I would recommend to follow the learn tutorial which details every step to create and use the API.
I hope this helps!!