Main from here
Connector Basics
About connectors
This refers to the component or devices used for electrically connecting and removing circuits and the like, and these can be easily connected or removed by hand and using simple tools.
These are used in various items such as smart phones, TVs, DVD players, notebook PCs, and digital audio players, and are indispensable components in the electronic products and electrical devices.
Neighboring devices include USB, LAN, and D-Sub connectors that connect to PC peripheral devices, and “optical”. “video terminal”, and “S-Video” plugs, etc., for TV, audio, and video.
They are also used, not only in things you can see, but even as board to board connections, etc., inside products.
Digital video cameras, digital cameras, washing machines, refrigerators, phone switches, semiconductor manufacturing equipment, pachinko-slot machines, etc.
Types of connectors

Board to board connections with electrical wires (board to wire connections)
Direct board to board connections (board to board connections)
Device to device connection (I/O)
Other (short connectors, IC sockets)
Connector image diagram (plug side)
Connector image diagram (socket side)
How connectors are manufactured
Product development
In product development, spring stress calculation and mating properties are simulated using 3D CAD analysis software. A prototype is made based on the results, and verification is performed with the actual item.
Tooling design
In mold design fabrication, a precision mold is designed using CAD based on the drawings designed in product development.
The mold parts are fabricated based on this design, creating an ultra-precision mold that determined the quality of the component.
Forming molds/formed parts
(housings, etc.)
Press dies/pressed parts
(contacts, etc.)
Forming machine (housing production)
Resin is flowed into the forming mold, making the shape.
Press machine (contact production)
Metal plates are punched by the press die, forming the contact shape. The finished contacts are then plated.
Assembly
The housing and contacts are combined, then the other formed parts and pressed parts are combined.
Products
The connectors are finished!