My usb port doesn't appear.

Using Arduino IDE 1.x
1

Your operating system: OS X Yosemite 10.10.1

What kind of board you have : Arduino UNO

Whether or not you were ever able to upload to the board. If so, what were you doing with the board before / when it stopped working, and what software have you recently added or removed from your computer?
It used to word on my mac. After 2 weeks I may updated my OS. And today I suddenly find the USB option in the port/tools is just gone. I double checked my JAVA, and reinstall the FTDIUSBSerial Driver 10 4_10 5_10 6_10 7. Reinstall the Arduino....Still don't work.

Arduino: 1.5.8 (Mac OS X), Board: "Arduino Uno"

2

Uno doesn't use FTDI chip, it has Atmega16U2 programmed as USB/Serial device.
Try pointing to the Arduino/drivers folder (but don't select the FTDI folder).

I don't have a MAC, so this may not be all you need.

3

Have you got a link to your exact board?