If you register a username for your Jami account, your JamiID will be that username, otherwise it will just be the account's infohash (public key fingerprint). A Jami username is a mapping between a unique human-friendly name and an account infohash.
> Is this JamiID that I created forever mine?
With the default Jami name server, https://ns.jami.net, username registrations are permanent, and cannot be changed or deleted. Also, if you delete or lose your account without having backed it up earlier, you will lose that username and it cannot be recovered. This is one of the reasons why it's really important to back up your account.
> If my friends create their JamiID, will the search just list them?
Yes, you can search others by their JamiID, whether it's their username or the longer account infohash.
> Do I need to import any JamiID's? How does discovery work for these JamiID's?
You would search for their JamiID and add them as contacts, similarly to how you would with other messaging applications. When you search a username, Jami will query the name server to get the account infohash and send a contact request. For example, with the default name server, to look up 'bandali' Jami would make a request to https://ns.jami.net/name/bandali to get the associated account infohash.
You can read more about this on the Jami user FAQ and the 'name server protocol' section of the developer manual:
How does this JamiID work?
Is this JamiID that I created forever mine?
If my friends create their JamiID, will the search just list them?
Do I need to import any JamiID's? How does discovery work for these JamiID's?
I'm seriously looking into Jami for "conference" calls with a small set of family members, it should be just point and click.