Even though USB connections are some of the most common connections across all types of cables and external devices, there's a lot of confusion surrounding the universal standard. There are many different types to consider, even though the more common products tend to fall into only one or two categories. The most common by far is USB 3.1, but what is USB 3.1?
USB 3.1 is a generational number that primarily refers to the data transfer speed of the USB connector, rather than its shape or size. Officially launched in July 2013, USB 3.1 (sometimes referred to as USB 3.1 Gen 2) has a maximum transfer rate of 10 gigabits per second (GBps). This is equivalent to 1250 megabytes per second (MBps). It replaced USB 3.0, which had a maximum transfer rate of 5Gbps and has been superseded by the still-uncommon USB 3.2, which has a maximum transfer rate of 20 GBps.
All of these speeds are theoretical maximums for the USB standard and unlikely to be seen in everyday use, but you'll definitely see increased transfer speeds for most file sizes when using USB 3.1 devices compared to using only USB 3.0 devices. USB 3.1 isn't supported by all modern devices yet, but it's slowly gaining support over the past few years. A good example of this change between different hardware generations is Dell's XPS 13 laptop. The 2017 XPS 13 9360 laptop shipped with two USB 3.0 ports, while the 2018 9370 version swapped out the USB 3.1 connection.
Another huge advantage of USB 3.1 is that it can support a feature called Power Delivery 2.0. This allows compatible ports to provide up to 100W of power to connected devices, allowing larger devices (such as laptops) to be charged via a single USB cable. This is most common in laptops that use the new USB-C standard.
USB-C is not the same as 3.1. Although often associated with USB 3.1, USB types such as A, B, and C refer to the shape and form factor of the port and connector, not the data transfer speed. Many modern devices have moved from traditional USB-A, USB-B, and microUSB-B ports to USB-C ports, and often use them with USB 3.1 transfer speeds.
USB-A is still offered on many devices to provide legacy support for older accessories and cables that still use the standard, but it's increasingly common for laptops and smartphones to use only USB-C connections.