where do i see usb connected device

The "System Info" (about this mac) should show the hardware,

and other items within the computer; including software list.

And Disk Utility, may show connected devices; depends on vintage.

Are you talking about a hard drive? If so it will show up in the sidebar of a Finder window. Scroll down the sidebar until you see Locations. If you select Preferences under the Finder menu in the menubar and select General you can indicate what items you want to appear on the desktop.

Depends on the type of device. External drives would appear in Finder on your desktop depending on settings.

Cameras would be found in app settings that can use them such as Facetime, or Photo Booth. Etc...

What type of device did you connect?

What is it you are expecting to see?