I'm a new client. I already uploaded my first project and I already have several proposals. If I accept one of them, how do I coordinate with the freelancer for the deliveries ? when and how do I make the payment ? what happens if I don't like the deliverables ?
re: "If I accept one of them, how do I coordinate with the freelancer for the deliveries?"
However you want. Upwork does not dictate those choices.
re: "When and how do I make the payment?"
If this is an hourly contract, then payment is handled AUTOMATICALLY. You do not need to do ANYTHING.
If this is a fixed-price contract, then the freelancer will submit work. You have two weeks to review it and request any changes if necessary (if the freelancer did not complete the agreed-upon task). If the freelancer has provided the required deliverable, then you can manually release payment. If you do nothing, that is fine too. Upwork will release payment automatically after two weeks.
re: "What happens if I don't like the deliverables?"
If this is an hourly contract, then you can simply close the contract and work with other people. You should only work with freelancers whose work you value the most.
If this is a fixed-price contract, then you need to see if the freelancer delivered what was agreed upon as a deliverable. If the agreement was "write a 1000-word article about widgets," and the freelancer provided a 200-word article about widgets, then you can click the "Request Changes" button and ask the freelancer to complete the task.
If the freelancer DID complete the task, but you don't like it, then you it is your responsibility to pay for the work. You may request changes, and the freelancer may make changes, but the purpose of a fixed-price contract is not to provide you with an endless supply of labor. The purpose is to hire a freelancer to create a specific deliverable.
For example: If the task is "draw a picture of a cat", and the freelancer does that... But then you decide you really want a picture of "a cat playing with a mouse"... Then you should pay the freelancer for her work even if it is not what you want. You should negotiate with the freelancer to either add a new milestone to modify the picture, or create a new picture. Or you could create an hourly contract that is flexible and allows you to ask for whatever you want.
Overall, I think one of the most important concepts for you to understand is that this is "freelancing." This is NOT "employment." This means you have an extreme level of freedom as a client. You can close contracts at any time, for any reason. Or for no reason at all. If you don't like the work that a freelancer is doing, just stop working with them. If that means that sometimes you pay for a bit of work that you can't use, that's neither here nor there. The important thing is to put your project first. You have no obligation to continue working with anybody if you don't like their work.
I think Preston did a really great job answering your first two questions. I'd like to shed some light on your first question: how do I coordinate with the freelancer for the deliveries ?
This depends on if you set this up as an hourly or a fixed-price project:
Hourly - Upwork's platform does not include any project coordination tools. Instead, they provide their own messenger application where files can be shared, and where you can communicate with the freelancer both before and after you hire them. Upwork is a way for you to connect and find freelancers. It's up to you, and your freelancer, to decide how you will work together.
Fixed Price - Similar to the above, with one minor exception. The freelancer may send the deliverables and ask for payment at the same time. You will have 14 days, I think, to review the deliverables before the payment is released.