The process of listing products depends on whether the product already exists on Amazon:

List products that already exist on Amazon

1. visit your products
2. click on the search glass icon next to the product you want to list
3. select the matching Amazon product from the list of search results
4. visit the feeds page - there should be a new pending feed
5. wait until the feed has been submitted - or submit the pending feed by clicking "submit feed"
6. check if there were any warnings or errors after the feed has been processed

List new products that do not exist on Amazon yet

1. enable the required categories in Settings » Categories
2. visit your products
3. tick the checkbox next to each product you want to list
4. select "List on Amazon" from the bulk actions drop down and click "Apply"
5. select a listing profile (see below)
6. check the prepared listings if everything looks all right
7. visit the feeds page - there should be a new pending feed
8. wait until the feed has been submitted - or submit the pending feed by clicking "submit feed"
9. check if there were any warnings or errors after the feed has been processed