Is this contact new to your account or already in the account on other lists?
If the contact is new to the account you can add them by clicking Contacts > Add Contacts > Type in one contact. Insert the contact's details and use the blue plus sign to add them to a new list.
If the contact is already in your account you can use the search tool to find them, click into their details, and use the blue plus sign to add them to a new list. An alternative approach to this is to find the contact in any list view, check them off and click "Manage Lists" in the header. You will be able to add them to a new list here.
Hope this helps,
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