many arduino programs-one processing program

hello…
could you please help me…
how to connect more arduino boards to one pc and control them by one processing…?
because i want to use more than 13LEDS

How are you talking to one Arduino? You open a serial connection to that Arduino.

You talk to two or more Arduinos the same way. Plug them in. Determine the port names that they are using. Open separate serial connections to each one. Write to/ read from the appropriate serial port to talk to the appropriate Arduino.

Of course, one Arduino can control more than 13 LEDs, using multiplexing, charlieplexing, etc. Even without that, you can use the analog pins as digital pins, so that gives you 6 more pins.

Of course, if you are using the serial port to talk to the Arduino, you can’t control LEDs on pins 0 or 1, so you’re down by 2 pins.

Another approach would be to use shiftregisters with your Arduino to give you more output pins to control your LED’s.

Check the playground for an example on how to use the 595 shiftregister to control many LED’s.