I cannot find a link to add seller/vendor/store in the Commerce-Marketplace module.
I am using Drupal Commerce Kickstart.
As far as I know, there is not a direct solution for this. I have searched google for this,couldn't find a solution. But I will share what I think is correct.
The store in commerce market place is actually similar to an organic group, where you can add members and products. The store is implemented as an entity. If you go to admin/structure/entity-type/commerce_store/store and add a store, you have created a store. Now, if you try to add a product, you can type the name of the store that you had created, which will auto-fill for you.
Regarding the vendors, you may have to create a role and give permission to create stores for that role.
Let me know how that goes.
as above answer its correct there is no direct solution for this . on marketplace websites there is main need is how to handle payment and drupal do not provide any feature like this there is some commits over pay pal chain payment but for drupal currently is in progress. I hope some one can make it batter