Can i connect extarnal hard disk to my lenovo all in one desktop?

Ok, past year i bought a lenovo all in one desktop pc which the model no: c320. Now i want to add a extarnal hard disk in my pc.in the time of purchased the seller told me that the all in one pc can't be upgraded. But now i think that many extarnal hard disk has USB connectivity & my pc also has usb port.so " Can i connect extarnal hard disk to my lenovo all in one desktop?"

Yes, if you have a free USB port, you can connect an external drive.
What the seller meant with his message that it can't be upgraded, is that you can't put in a different graphics card, add a network card, internal disk, etc.

If you run out of USB ports, you can also buy a USB hub that will allow you to connect more devices.

Provided that your PC has a USB port then you can connect any USB external hard drive to it.

Yep you should be able to unless there's a hardware problem.