problam uploading board

when i want to upload this erro is shown
Arduino: 1.8.5 (Windows 10), Board: "Arduino/Genuino Uno"

Sketch uses 1938 bytes (6%) of program storage space. Maximum is 32256 bytes.
Global variables use 202 bytes (9%) of dynamic memory, leaving 1846 bytes for local variables. Maximum is 2048 bytes.
avrdude: ser_open(): can't open device "\.\COM3": The system cannot find the file specified.

Problem uploading to board. See for suggestions.

This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.


the port is unavailable in tool
and my arduinos led are on

If the port menu is grayed out, com ports are not detected and during upload the IDE will use the last one that you did select.

What happens in Windows device manager when you connect the board? Does it recognise a board? If so, any yellow triangles?

Is this an original Uno or a clone? For the latter you might have to (re-)install the drivers.