Astro ID is an account for you to manage your Astro services seamlessly online. Anyone can make an Astro ID (including non-Astro customers), but some services/portals require you to have an active Astro subscription in order to sign-in and use their web or app services.
For active Astro subscribers, your package might also come with access to selected streaming apps. These apps might require an Astro ID to activate and log in. Please check your subscribed package with My Astro to know further.