Different individual, different observation. Different day, different observation.
Some people choose to add multiple observations for something like multiple individuals in a nest, so that you can annotate one as the egg or baby and one as the adult. But plenty of people will just add one observation instead of splitting it out. Your choice.
The Getting Started guide and the FAQ page are the two main intro type pages for the website. (There is a short tutorial on the app, but it’s very simple.)
https://www.inaturalist.org/pages/getting+started
https://www.inaturalist.org/pages/help