Your payment method is verified? You are set to go then!
Have you already found the freelancer you want to hire? Had you posted a job yet?
If yes, there are two main ways to go about it.
The easiest is probably to go to the Upwork profile page of the freelancer you like, and just press the "hire" button like so: http://prntscr.com/877oqv
If the freelancer has applied to your job you can find the hire button on the applicant's details.
When you say "you can't" - what happens when you try?
In case it says "Offer creation failed" when setting up a fixed rate contract chances are you need to check your payment method, as that usually means the charge for the funding of the first milestone didn't go through...
Ask if you have any further questions!
Hi Ben and welcome to Upwork!
I see that you have already messaged some applicants and ready to make an offer. There is one thing you need to take care of before sending the offer - please, complete your Company Information. You can do it by clicking on your picture in the upper-right corner and navigating to your Settings. Click edit to input your company's address.
You should be able to make an offer to a freelancer then.
As is typical, the OP hasn't logged in for 7 hours to check replies.
I seriously hope that this client got an email from Upwork, because very often these users never return to the forums.
Possibly because they think THIS is support, and that they will get an email (like they would if this was Zendesk) in reply to their "post".