One of two usb ports on Mac Book Pro does not working.

For an Intel Mac—

Try resetting NVRAM/PRAM http://support.apple.com/kb/ht1379

(get at least two-three rounds of the chimes when holding the NRAM Reset)

if no resolve

Try resetting the SMC https://support.apple.com/en-us/HT201295

If this is a hardware problem you can try run the user Diagnostic...not as definitive as Apple's own AST2 (Apple Service Toolkit) back bench diagnostic, but may kick out an error code.

Use Apple Diagnostics to test your Mac

https://support.apple.com/en-us/HT202731

Otherwise your best bet is take it in—

In or out of warranty you can get a free over the counter 'Apple Service Diagnostics' test /assessment

Make an appointment for a "hardware issue"—

https://www.apple.com/retail/geniusbar/

Outside the USA

https://locate.apple.com/country

If rebooting the laptop and resetting the PRAM does not work, then you most likely have a hardware failure with the laptop. If the USB port on the left side is not working, then that is an expensive repair since that port is part of the Logic Board. If the right USB port is not working, then perhaps the I/O Board or I/O Cable is bad or loose.

You may want to check the bad USB port on the laptop to make sure there are no bent or damaged contacts or a piece grounding shield is not bent preventing the USB cable from fitting all the way into the port.

However, a 2014 laptop is considered "Vintage" by Apple. Apple will repair a "Vintage" Mac as long as the necessary part(s) are still available.

Model year of the MacBook? Two or Four Thunderbolt?

We need more information.