If you have a client account in Upwork, you can see a big green button on your dashboard says" POST A JOB". If you don't see anything like this, I am afraid you are registered as a freelancer, not a client.
It's not a problem though. You can still create a client account. To do that follow the steps below:
1) Click on the drop-down menu at the right corner just beside your avatar and name
2) Go to Settings > My Teams and choose the "Create New Account" at the bottom.
3) Choose "New Client Account."
and follow the steps to complete the process
Once set up, click on the drop-down menu at the right corner just beside your avatar and name to switch between your client account and freelancer account. And then you can see the"Post a Job" button from your client account.
Hope this will help.
For you to be able to post a job and hire freelancers, you'll need to have a client account. You can be both a freelancer and a client on Upwork. You will use the same account to log in to Upwork but will have two separate user profiles. You will be able to easily switch between the two as needed.