This PHP code loads data from a MySQL database based on a selected purchase order (P.O.) number. It displays key information about the P.O. such as the supplier, order date, arrival date, list of products with codes, descriptions, quantities, categories. It also calculates and displays subtotals and totals for product quantities by status (initializing, declared, cancelled, cancelled due). The code uses multiple SQL queries to retrieve the data and populate the HTML table for display.