Firstly you need to install it on your shopify store, you can do that by following this link: https://apps.shopify.com/feeds-bridge
Once installed, go to shopify apps tab and select Feeds Bridge application, you will be redirected to application page.
Then you will need to set up your vendors, you can do on "Vendors" tab on application page.
Once vendor is created and it's source file is defined (you can either provide ftp access during vendor creation or select local file) and file selection action button will appear under that vendor line on vendors tab.
Then you need to define file map, there is a separate tab for "file maps" management, when you go there select vendor, click on "Update file headers" button (this action will read all the headers from your file) and start mapping file fields to system fields. Map will be accepted only when all required fields are mapped.
Only you have your map defined, you can go back to vendors tab, select vendors you want to import and click import under actions menu. If your vendor is enabled catalog export will be triggered right after import is done.
This is the most basic way to use feeds bridge application, there are additional features which requires additional actions, like template validation, when it's enabled vendor items will only be exported when it pass template validation, example you have an items with item type "Ring", but it doesn't exist on your template, in that case such item will not be exported and "Template fail" error will be displayed under that item. In this case you need to either create new item type un der template tab or create an alias for that string to refer those items to another item type, example you have item with "ring" type but you prefer to accept only item type "Rings" then you create "Rings" item type and create "Ring" alias in that case all "Ring" type items will be exported as "Rings".
You can also use pricing rules functionality (in case you don't have final prices and compare at prices on your catalog feed) once this feature is enabled (sugested to use with template validation on because you will have more structured item types), pricing data will be read during catalog import and you will be able to start creating pricing rules for that vendor. Rules are created based on item type, min and max price ranges. So each item type may have multiple rules for different price ranges.
Also There are video tutorials on application Help page, so you can take a look at those as well.
