Dear ambition,
If both PICs have a built-in USART peripheral, are physically close to one another, and operating at the same voltage, you may connect both PICs together directly using the TX and RX pins (crossed between PICs)... If the distance is greater or if the PICs are located in an electrically noisy environment you may wish to connect the USART ports together using RS232 or RS485 interface ICs...
You can also "bit bang" asynchronous serial data using 1 or 2 pins or "bit bang" synchronous data using 2 or 3 pins...
I suspect there are many many different ways to convey data between two PICs... I hope I may have provided you with some useful ideas...
Regards, Mike