How do PC companies like Asus and Dell make laptops?

first of all production is something bigger than this,companies like dell for example,are buying from companies that actually make chips,semiconductors etc,or even by the whole parts for instnce their laptops mobo from another company or they make it their own,dont know about that and it doesmn't make any difference because they buy the means to make their laptop

Well all laptops are manufactured by ODM's (Compal, Quanta, Foxconn, Wistrom) in Taiwan and China except Lonovo manaufactures a model here. Dell, Toshia and Apple are OEM's. Typically the OEM's design the laptop and the are built in Asia or China. They use parts made by companies like Intel, Seagate, Nvidia, Realtek to build the laptops. MSI and Asus are ODM's and OEM's as they started with their own brands maybe 10 years ago as there were price wars between OEM's and ODM's. MSI and ASUS also make motherboards that the other OEM's use. MSI and Asus also make what are called barebone system that is basically a case and motherboards that are sold to places like ExoticPC where components (HD, memory and other components are configured by the customer. The you have ODM Clevo (know for high powered gaming machines) that sell there cases to companies like Sager and Prostar and they place their brand the computers and allow customers to configure to their own needs. Clevo's are sold with unbranded and they are called barebones. Also the laptop syou buy at Best Buy, Newegg and Tiger Direct are sold as configured in the factory and any modification is post sale and subject to typical parts and labor charges like the Geek Squad does. In other words Best Buy cannot modify a factory configuration to display in their stores.

I once bought a HP laptop and the tracking went from Shanghi to Alaska to Chattanooga then to Florida.

Also Quanta manufactures machines for Dell and Apple so you may see model that resemble the other OEMS. Also Dell may use one ODM for the XPS line and another for the Inspiron line which make them look completely different.