Uno upload problems

I have Arduino Uno R3.

I plugged it to Mac via USB. What i should choose in Tools>Programmer menu?

When i try to upload nothing happens and rx/tx leds don't blink.

I get error: "avrdude: stk500_recv(): programmer is not responding"

My network settings might be wrong. It seems to use Apple Internal Modem.

I can't find information what stead/blinking leds mean.

You shouldn't have to go to Tools > Programmer

Go to Tools > Board and make sure your Uno is selected, then go to Tools > Port which should show a list of available ports - your Uno is likely the LAST item in that list, so select it and then try to upload your sketch again.

So i can set Tools>Programmer to anything and it should work?

Board and Port is set correctly but uploading still fails.

Where i can find out what those (blinking) leds mean?