Connector Basics

Connectors are used to join subsections of circuits together. Usually, a connector is used where it may be desirable to disconnect the subsections at some future time: power inputs, peripheral connections, or boards which may need to be replaced.

USB connectors come in two flavors: host and peripheral. In the USB standard, there is a difference between the two, and the connectors on cables and devices reflect this. However, all USB connectors will have some things in common: 

Polarization: A USB connector can only nominally be inserted one way. It may be possible to force a connector in wrong, but that result in damage to the device. 

Four contacts: All USB connectors have at least four contacts These are for power, ground, and two data lines. 

Robust power connection: It’s important for the power pins to make connection before the data lines, to avoid trying to power the device over the data lines. All USB connectors are designed with this in mind. 

Molded strain relief: All USB cables have plastic overmolding at the connector to prevent strain on the cable that could potentially damage the electrical connections.
More about connectors, you can leran from EPCB Blogs