The Export.gov website has been replaced by Export Solutions from the ITA.
It provides a very good outline of the process to follow for finding tariffs (aka duties), which can be expressed either as rates or as fees, depending on the product. However, their pages also include some broken links, and occasional circular linkages! I've pulled out some of the pages I think will be most useful: they are below.
Time constraints? Consult the World Tariff Profiles book, linked below.
For a better understanding of the process and issues: start with these two pages from Export.gov.
In the US, there are two main classification systems used in the trading process:
Both are based on the Harmonized System (HS) created and maintained by the World Customs Organization.
A Schedule B code is necessary for finding out tariff information!
Below are links to two duty non-governmental calculator sites, one of which is mentioned in the how-to video below. Finding the link to CUSTOMS Info on the original Export.gov page is difficult, because that page has been updated since the video was created, so I've linked to it here.