When submitting a package to the concrete5 marketplace, first you will need an account on www.concrete5.org. Once you have created an account, you will have to fill out a form (located at http://www.concrete5.org/marketplace/manage_item/) containing information about your package:
You will fill out all of the marketing copies that will appear in the marketplace listing, as well as some internal meta data about your add-on.
Once you have submitted the add-on, some automated tests will be performed on it to see if it meets the eligibility requirements. Once the add-on passes these tests, members of the Peer Review Board (PRB) will take a look at your add-on.
The PRB is a group of volunteers from the concrete5 community. These volunteers are responsible for testing every add-on and theme that is submitted to the marketplace. They will install your package on their own version of concrete5 and test it fully to make sure it will work without difficulties, and to ensure that your add-on adheres to the rules.
concrete5 allows developers to sell their add-on. The lowest price you can set for an add-on (other than free) is $15 USD. concrete5 will keep 25 percent of your add-on's revenue, but the exposure they provide to your add-on by featuring it in the marketplace is usually worth a small commission.
If you sell an add-on in the concrete5 marketplace, you will be expected to support it. If your add-on doesn't work and you do not provide support for it, concrete5 will refund the customer and also charge you a 15 percent penalty. Make sure you are prepared to invest the time in supporting your add-ons.