Um, search ? There's a thread stickied near the top of Q&A titled 'Flash Stock firmware/ROM + Root...' that has a simple root method, there's also a bunch of guides stickied near the top of the General section. I mean, this phone was released almost 3 yrs ago, 'how do I root ?' has been asked answered thousands of times already, and that's why we have stickied threads (so we don't have to regurgitate the same stuff over & over for n00bs who won't search).
And if your next reply is 'but it doesn't mention anything about 'l9100TDVLS3 build num: JZO54k,l9100TDVLSM Model num: GT-l9100T', you obviously don't understand what you're about to do & I suggest you read the guides/tutorials I mentioned above before you do anything lest you break your phone.
If it's important enough to cause you grief if it's lost, back it up. No excuses
Trolling for thanks is lame
Does Samsung's auto-brightness implementation crap drive you to self-harm ? A solution !
Probably the best thread ever posted on XDA
Failure to search is the leading cause of male impotence on XDA
If you don't know how to recover if things go wrong, what are you doing flashing custom roms ?