According to a blog post by Twitter, to use this feature you need to log into TweetDeck with your Twitter account instead of the earlier legacy TweetDeck account, which had a log-in via an email id and password.
With the introduction of TweetDeck teams, once you log into an account, all you need to do is go to account and type the name of a user who you want to give shared access to for an account. For instance, if you run a website and you want all your team members to handle the account for that site, just type in their account name and select authorise.
One you do that “an email will be sent to the account,” that you’ve chosen and they will need to accept the invitation to get access. Once they do, you too will receive confirmation on your related email account that your team member has been added a contributing partner.
According to Twitter, “If you’re currently sharing your account, you can change the password and revoke app access to ensure that from now on only the people you’ve just added will have access.”
The person (the owner of the account) who knows the password can add or remove team members, view the team and access the account from non-TweetDeck platforms (e.g., Twitter.com, Twitter mobile apps). The owner can change passwords, credentials, etc. Other than the owner, roles on TweetDeck teams will be divided into admins and contributors.
Where admins are concerned, they can sign into TweetDeck with their personal account and then tweet from the official account account (plus build lists, follow or unfollow accounts, send Tweets and schedule Tweets), add or remove team members and view the team. An admin however cannot access the account outside TweetDeck or change the credentials or password. Contributors can tweet from the account but cannot view, add or remove team members, and can not access the account outside of TweetDeck.
For those who don’t want to receive invitations to others’ teams, they can opt out completely on twitter.com/settings/security.
The good thing about this is that if you have many team members accessing the account you can ensure that not everyone has the password. If someone leaves the team, you don’t have to keep changing the password each time and it also makes account security slightly more reassuring.
However Twitter also cautions that you must continue to “use login verification on your accounts” and encourage team members to do that same, since control over a password doesn’t mean complete security on the Internet.