Creating an account on the Career Center as an employer is separate from any membership accounts with the association directly. You can typically tell if you're a member or not by checking if you or your organization are paying membership dues. If you are not yet a member and are interested in taking advantage of member benefits on the Career Center, you would first have to establish a membership with the association.
You can click on the association's logo at the top of the page and be taking to their website. Many associations will have a tab at the top of their page where you can learn more about membership options and how to join. If there is not, or if you have further questions, you should be able to pull up contact information (often at the bottom of the page) where you can directly inquire with the association on membership requirements and fees.