Help for a begginer topic

Im Sorry guys to bother you but i need to root/flash custom roms and modify some stuff in my sister's galaxy w and i dont know anything about samsung system because im using sony since i was born and the system in sony was that i have to unlock bootloader then root then flash kernel then flash custom rom and if something goes wrong i hold the volume up and go into fastboot mode and get everything back to normal
So please if anyone can help me on how to root and flash and what are the right steps and if i got into a bootloop or something how can i get the phone back to stock
thanks in advance