You can manually type the email addresses of recipients in the To, Cc, or Bcc fields as you need, and separate these recipients with semicolons.

If you have enabled the Use Auto-Complete List option in Outlook, it will pop out the auto-complete list based on the characters you typed in the To, Cc, or Bcc fields. And you can pick up proper recipients from the auto-complete list directly.

Tips: The Use Auto-Complete List option is enabled by default in Outlook. If the auto-complete list option is disabled, you can enable as follows:
(1) Click File > Options;
(2) In the Outlook Options dialog, click Mail in the left bar, check the Use Auto-Complete List to suggest names when typing in the To, Cc, and Bcc lines option in the Send messages section;
(3) Click the OK button.

You can also add recipients from existing address books in Outlook. Please do as follows:
1. Click the To, Cc, or Bcc button to open the Select Names dialog.

2. In the Select Names dialog, please choose a certain address book from the Address Book drop-down list, select one or multiple contacts (or contact groups) as you need, and then click the To, Cc, or Bcc buttons to add selected contacts as corresponding recipients.

3. Click the OK button.
Tips: If you add a contact group as recipients, you can click before the contact group to expand the group in the To, Cc, or Bcc field.

1. In the mail view, click Home > New Email or press Ctrl + N keys to create a new email and open the message composing window.

2. If you cannot find out the Bcc line the message composing window, you can add the Bcc line by clicking Options > Bcc.