If you are an Account Admin for your organisation. You can create new members yourself. simply click your name in the top right corner of any page in Portal, select "my profile" to access your profile information and under the "Manage Users" tab select "Add User". When you create a new user, a confirmation link will be sent to their email where they can set a password for their new Portal account.  

Alternatively if the person has already created an account (For more information on how to do that, click here.) you can add them as a user directly on your station page(s).

Navigate to “Users” on your station page and click the green “+” button. From here, type in the email that your new user used to register and determine their user level (See User Permissions). Your new user is now all set up to use Portal for your station!