Can't upload Blink sketch into arduino uno

Hi, I just bought the starter kit recently and when I tried to upload the Blink sketch into my arduino uno, I got the following error message. I am using my MacBook and the latest arduino IDE. The board, serial port and the programmer are selected correctly.

"avrdude: verification error, first mismatch at byte 0x0000 0x0c != 0x00 avrdude: verification error; content mismatch"

When I tried to use "upload using programmer", the error message changed as before.

avrdude: usbdev_open(): did not find any USB device "usb"

Please help me.