I checked your account, and I can see that you have already sent an offer to the freelancer. Once the freelancer accepts the offer, it will become an active contract. The freelancer can then start working on the project by tracking his hours using the Upwork Time Tracker App. The hours logged are available for you to review by checking the work diary. To learn more about Paying for hourly contracts, please check this help article. For more information, please check this help article: Review Your Freelancer's Work Diary.
I'd also encourage you to read the client section of this post to help you learn more about the process as a client on Upwork.