It depends what device you are talking about.
If it is a desktop computer, there are usually several USB ports on the back panel where the motherboard's ports come out. Many computers put one or two USB ports on the front panel
If it is a notebook computer, the ports may be on either side of the machine or on the back.
USB 2.0 and 3.0 ports are rectangles about 13mm wide and 5 mm high, these are called USB A Female ports. The ones with blue plastic inserts are USB 3.0 speed. the ones with black inserts are USB 2.0
There is a new USB port called Type C. it is smaller, a slender rounded port about 7mm wide. With the correct cable, you can adapt from USB - C to USB - A type. You will see USB C ports on only the most recent machines
If you are talking about a device like a printer, smartphone or camera, then there is more variability.
USB ports on printers and large external devices tend to be a squarish, 10 mm x 10 mm USB B-Type port, there are 2 versions, USB 2 and USB 3 which has an extension on one edge, These can usually be found on the back panel or at the back of a side panel.
USB ports on most phones and cameras are Micro USB which is about 7mm x 2 mm with one of the long edges bevelled. These are common for charging ports as well as USB data.
A few newer smartphones are using USB Type C ports.
Most Apple iPhones don't use USB at all but use a "Lightning" port.
Older devices may have Mini USB. Some devices that need more power such as external hard drives, mayhave a Micro USB 3.0 which is wider than the MicroUSB and has more contacts.
Cameras often have the ports hidden behind doors or rubber gaskets. Cellphones most commonly have the USB port on the lower edge.
Diagrams of the different cable ends and much more data is here https://en.wikipedia.org/wiki/USB