In order to apply for a posting, you must login with your applicant profile username and password.
Refer to: How do I create an Applicant Profile? or How do I log in if I have already created an Applicant Profile?

Apply to a Posting

Once you have logged into your Applicant Profile, click on the button at the top of the screen.

All current job postings will display. Click on the button to apply to a posting. You will receive a confirmation asking if you are sure that you want to apply.

You can apply to a posting up to and including the date of the posting deadline.

Withdraw from a Posting

Click on the Withdraw button to withdraw your application from a posting. You will receive a confirmation asking if you are sure that you want to withdraw.