@Kumaranath Fernando You need to Navigate to the Products of your APIM instance and add/select an existing product and customize it according to your needs. Please refer to this document on how to create and publish the product. You can add the API's and define the access control on your products. In your case if you want user to view the API as the Guest then you need to add the API to your product having the "Guests" Access Control.
Feel free to get back to me if you need any assistance.