What is the AspNetUserLogins for?
In Asp.net Identity, the Identity system uses the AspNetUserLogins table to hold information about 3rd party/external logins, for example users who login into your site via Google, Facebook, Twitter etc. The AspNetUsers table is the primary table to store user information, this is linked to AspNetUserLogins via UserId -> AspNetUsers.Id.
For example if the user logs into your site via Facebook, then the LoginProvider is the name of the service which provided the login, so in this case "Facebook", the ProviderKey is a unique Facebook key associated with the user on Facebook.
This table is used by the Asp.net external authentication providers.
Is it to store the logins from the user?
No not really, it is used as explained above
How can I then update this table with that data?
You don't update the data in this table, usually when a user logs in via external provider, after user has been authenticated, the provider returns a ClaimsIdentity, which has users claims and one of those is a unique id of the user in the external provider, this gets automatically updated in this table.
read more about external providers here
