After i upload the GRBL code i will be able to run G-Code .txt files?
GRBL needs to be sent the G-code commands one at a time over a serial link and will respond when each one is complete
To quote from Frequently Asked Questions · grbl/grbl Wiki · GitHub
How do I stream a complete G-code program to Grbl?
Streaming g-code programs to Grbl may be done by a simple send-and-respond method through the serial port. Every command followed by a return is responded to when Grbl is ready to receive another command.
Will l be able to have some comunication like Master/Slave?(using grbl code)
I want my slave to execute the G-code.
GRBL does not care what is sending the commands so they could come from a second (master) Arduino that reads them from a file and passes each in turn to the slave Arduino to be executed when it is ready.
Do i need any farther sources?(shield,drivers etc.)
Yes, of course you do, as an Arduino is not able to control a stepper motor directly.