Hi Alex,
A feature collection can be published to a feature service at any time (with an organizational account), by going to the details page and selecting publish.
When you create geographic data from a csv with under 1000 records directly in the Map Viewer, it automatically creates a feature collection. To create a feature service when publishing directly from a CSV file, you will need to add the csv file to your content and follow the prompts to publish a feature service.
A feature collection and a feature service have very similar functionality, depending on how you are going to use your data. For small datasets (less than 100 records) that can only be edited by the owner of the data, a feature collection can be very effective and easy to create. If you are looking to be able to have multiple editors and download/export the data in various formats, than a feature service will have the correct functionality.
Thanks,
Kelly