The former Real Madrid star, 33, was unveiled by Juve on Monday.
“In my opinion Juventus is one of the best clubs in the world,” Ronaldo said at his presentation Press conference.
“It was a well thought through decision, and my friends and teammates told me for a long time this was a club that would suit me.
“So it was an easy decision given the power and size of the club, it’s the biggest club in Italy.
“There are outstanding directors and an outstanding Coach [Max Allegri] and a great President [Andrea Agnelli] who is used to winning, so it wasn’t a difficult decision in that sense.
“I enjoy football, I’m still quite young and I’ve always liked challenges in my life: from Sporting, to Manchester United, to Real to Juventus.
“I’m not sad [about leaving Real Madrid], this is a big club and with all due respect players at this stage of my career usually go to Qatar or China.
“So I’m grateful to Juventus for allowing me to join such a big club.
“My nine years in Madrid were beautiful but this is a brand new step in my life. I thank the supporters with all my heart, but I have to focus on this new challenge.
“I’ll try to show that I’m a top player, I’m going to work hard and I’m very ambitious. I don’t like to stay in my comfort zone, I like to seize new challenges.”