Arduino to Arduino

How can I connect two arduino(s) together. I heard if you connect two arduino together, it would make a dual core processor?

uhmm a Dual-core Arduino doesnt exist.

and connecting 2 arduinos by I2C doens make it Dual-core.
i think you can say it becomes a Dual thread system.

How can I connect two arduino(s) together.

I2C up to 128 arduinos can be connected.
or Serial. RS232 i think but only 2 arduinos can be used.

I2C, SPI, Serial. With Serial, can connect Rx to Tx, Tx to Rx, Gnd to Gnd. Lots of options for connecting more than one; RS485 is good, all connect in parallel; one talks, others listen, one replies.

Can put 2 Atmega328P on one board. One can be IO to user, and 2nd can do dedicated tasks as directed by first, with as much or as little interaction as you want to program in.

http://www.crossroadsfencing.com/BobuinoRev17/

Saarisht: How can I connect two arduino(s) together. I heard if you connect two arduino together, it would make a dual core processor?

If you want useful advice tell us what your project is.

...R