The wicket-keeper will lead a side wihout regular captain Rahul Dravid and fellow senior batsmen Sachin Tendulkar and Sourav Ganguly, all of whom have opted out of the tournament.
Dhoni, who made his international debut only in 2004, told reporters at The Oval, where the third and final Test against England starts on Thursday with India 1-0 up in three-match series: "It's a pleasure leading your country especially when you are just over three years old at international level. "Coming from a state that's not very renowned for cricket, five years back nobody thought somebody would play for India from this state.
"So now if I look back, I'm very glad, I'm very happy, I'm excited," the hard-hitting batsman added.
And he said his elevation would mean a lot for all those connected with cricket in the eastern state of Jharkhand.
"It is not very renowned for cricket and I am like a brand ambassador for them, coming from a small state where the infrastructure is not so great for cricket. But work is going on there to improve cricket."
India have played just a solitary Twenty20 international, a six-wicket win with one ball to spare against South Africa in Johannesburg in December.
"We have just played once (in Twenty20), it's very challenging. But the only good thing is we had a domestic Twenty20 circuit this year and the teams have done pretty well over there.
"But when we go to South Africa the conditions will be very different, the ball will do a bit. It won't be as easy. There will be different challenges on the way. We need to plan and adapt."
And he said his lack of captaincy experience would not count against him. "I never had the experience of playing at international level until I played my first match.
"But if you are eager to learn and very open-minded you can learn a lot from the senior players," he added.
Dhoni, 26, who has played 19 Tests and 76 one-day internationals, said India could still be a force in South Africa despite the absence of their trio of batting stars.
And he was adamant the lack of a full-time coach, something the side have been without since Australia great Greg Chappell decided not to seek a renewal of his contract following India's first round World Cup exit, would not be an issue either.
"We have Robin Singh (fielding coach) and Venkatesh Prasad (bowling coach). Experience wise, Virender Sehwag is there, Yuvraj Singh is there and Ajit Agarkar is there.
"It's not like we are lacking anything. We have players who have played more than a hundred one-day international matches. Their experience will count."