Below are some helpful links to get you started:

CBP has some resources here: https://www.cbp.gov/trade/basic-import-export

Every item requires a Harmonized Tariff System (HTS) code. Here is the current HTSUS: https://hts.usitc.gov/

CBP maintains a public repository of requests for classification assistance here: https://rulings.cbp.gov/home

Informed Compliance Publications (ICP) cover a variety of sticky Customs topics and classifications: https://www.cbp.gov/trade/rulings/informed-compliance-publications

Unstacking certain tariffs chart: https://www.cbp.gov/document/fact-sheets/unstacking-certain-tariffs-chart

CBP Forced Labor info & portal: https://www.cbp.gov/trade/forced-labor