To sync the newly created product from Marketplace to SelluSeller follow below steps:
Go to Marketplace Management --> click on sync product button to respective Marketplace --> newly created products will get synced.
Note: products will sync automatically only for the first time when you connect Marketplace with SelluSeller, post that you need to manually sync products by clicking on sync product button respective to Marketplace.
Click here to know how to create a product and list on Marketplaces.
Hope this answers your question!