It’s not easy to setup. In order to add all the market place attributes you need to create import CSV files that you can import to Ecomdash unless you are willing to type it in manually, or you can download them from the marketplaces.
It will list new products to the storefront. However, if you already have listings on the marketplaces you can import some of the attribute data by importing or downloading as they call it. Then you can work with the data and update it in ecomdash. But sadly you are not able to update active listings from ecomdash which makes it hard to work with.
In order to delete an item you first must manually delete it on ALL the marketplaces before you delete the item in ecomdash.
In order to keep data current, especially the quantities, you must download from the marketplaces frequently. But this process will not only update the quantities but also overwrite you attribute data from the marketplace to ecomdash.