Thank you for this question. You might want to share this help article with your client for more information on how Escrow work on the Upwork. Also, you can send the link to your profile to your client, so that they can or send you an offer by clicking "Hire Now." Sending an offer on a fixed-price job requires them to deposit funds for either the whole contract or a lesser amount to cover the first milestone. This deposit will be held in escrow until they receive the work, are satisfied, and release funds to you.
I hope this helped. Feel free to reach back if any further assistance is needed.