The 21-year-old striker put pen to paper on a three-year deal at City Ground on Saturday afternoon, bringing an end to the recent speculation over his future.
Cummings, who is understood to have cost the Reds around £1m to sign, admits to being upset at leaving Hibernian but is looking forward to fighting for a place in Forest's starting lineup ahead of next season.
"I am absolutely delighted. It is a massive club and a great opportunity for me," he told the club's official website. "Obviously I am gutted to leave Hibs as I enjoyed my time there but I just feel it is the right time to move on and further my career. It is a massive club and I played against the manager's team a couple of years ago and I like the way they played.
"I had a couple of mates in his team then and they only said good things about him so I am looking forward to playing under him. I want to play football and score goals and the way that the manager's teams play, they normally create a lot of chances so I feel that I am in the right team to create chances and hopefully I can get a few goals.
"I have heard a few from a few of my friends, who have come down here to play, about English football but obviously I have never played in England so it is all new to me. I think I will adapt to it – the goals don't move as they say.
"I'm not coming here to just walk into the team. I have come here to learn as I will be playing with, and against, a lot better players so I am still at the learning stages and, with the gaffer here, I will only get better."
Former Scotland Under-21 international Cummings netted 69 times in 148 matches for Hibs in all competitions.