Once the user has a session for the Okta org itself, they can use it to log into any applications they are assigned without needing to re-authenticate, via SSO. This is reliant on the user’s session cookie (set on the Okta domain when they log in) being present in their browser at the time the /authorize request is made.
For example, after user logs into App A via an /authorize redirect, they can then log into App B, C, D, E, etc when they each (since each application has its own set of tokens) make their own /authorize redirects, but unless the policies in your org require the user to re-authenticate, they will not be prompted to complete primary authentication again
You would need to make a redirect to the /authorize endpoint to do this (since SSO is reliant on the user having a session cookie in their browser). The parameters for the /authorize call will depend on what grant type each application is using.
yes, each application needs to make its own /authorize request with its own client_id included in order for them each to receive their own set of tokens