Both players made their Toffees' debuts against Chelsea on Saturday when the Merseysiders won 1-0 thanks to a Steven Naismith header on the stroke of half-time.
And McCarthy praised Barry for his performance at the weekend, telling the Liverpool Echo: "He is brilliant.
"He got about, chased Chelsea down and never stopped harassing them. It will be a huge boost for me to play alongside him.
"He always wanted the ball and was looking to play passes all the time. Even his clearance was outstanding.
"I've only trained with him a few times but already he's been talking to me a lot and he's a joy to work with.
"Obviously, I'll learn a lot from training with Gareth."
As for the game with Chelsea, McCarthy added: "The gaffer said I'd get a chance and I enjoyed it even if it was a difficult game. I'm just glad we got the points.
"It was a hard game to come on in. It was just about seeing it out at the end.
"The atmosphere was different class. As a kid you dream about playing in front of big crowds at places like this. The fans got right behind the team and they were brilliant."