If you mean SPI or I2C:
Set GIE/GIEH (bit 7 of INTCON register). Set PEIE/GIEL (bit 6 of INTCON register). Clear SSPIF (bit 3 of PIR1 register). Set SSPIE (bit 3 of PIE1 register). That's the setting for interrupt. Set up the MSSP module for required operation. Do the necessary actions in the ISR (Interrupt Service Routine).
If you mean UART:
Set GIE/GIEH (bit 7 of INTCON register). Set PEIE/GIEL (bit 6 of INTCON register). Clear TXIF (bit 4 of PIR1 register). Clear RCIF (bit 5 of PIR1 register). Set TXIE (bit 4 of PIE1 register) for transmission interrupt. Set RCIE (bit 5 of PIE1 register) for reception interrupt. Set up the USART module for required operation. Do the necessary actions in the ISR (Interrupt Service Routine).