I checked and it looks like you have a Freelancer account right now. In order to post jobs, you can create a client profile for your account, you will use the same account to log in to Upwork but will have separate user profiles.
Go to Settings > My Teams and choose the Create New Account button at the bottom.
Choose New Client Account
Once set up, use the account menu at the top-right of your screen to switch between using Upwork as a client, freelancer, or agency