Hey!
GGL is very good for PvP.
Personally, I've gotten R1 with it many times. Gladiator almost every season. Cutting Edge every raid, 3K+ io the last couple of seasons...
Unfortunately, Rogue is one of those classes that unless you use an internal rotation, it's going to be challenging to push gladiator or higher
unless you have a very good understanding as to how it works.
Many classes the rotation can carry you to glad, but Rogue is not one of those do to it's CC complexity.
Nevertheless, if you are comfortable with Rogue and you can manage some manual input, you need to buy the following things -
"Retail Rogue" from GGLoader.com (one time payment)

- click, then scroll down to "Gladiator Rogue" (monthly payment).
After that, you'll have to buy a GGL subscription after your first month.
As for setup, there are video instructions, plus Spiken just released an autobind feature so you can be up and running extremely quick.