My ambition is to have them back top where they were in the years of (Sir Alex) Ferguson, he told reporters in Amsterdam as he flew out to Portugal with the Dutch national squad for training camp.
I have always had a winning mentality and will find a system to make sure we are not beatable.
They are hoping I can do it in my first season. I did it in Spain (with Barcelona) in my first season and I think I can do it in England too. I think it is a difficult task but a fantastic challenge.
At such a big club it is always going to be difficult but Im very happy to have the chance. I said last October that Id like to coach in England but I never thought it would be with the biggest club in the world.
The 62-year-old Van Gaal said he was already in deep discussion over new signings for next season but refused to confirm he had been handed a considerable budget to strengthen the team after a disappointing season.
Ive havent talked to them (the club) about money, only over the players that I would like to have and those that may leave," he said.
Asked whether his first signing might be Dutch midfielder Kevin Strootman, who will miss the World Cup because of a knee injury, he added: Thats for you to ask and me to know.
Van Gaal hinted at his frustrations over recent weeks as mass media speculation about his move to Old Trafford had to be met with unconvincing denials.
Its a process and I couldnt tell what was happening. I found it frustrating because for several weeks I have had to peddle no's when I am, in general, usually open-hearted, he said.
The World Cup-bound coach, who last year announced his decision to quit the Dutch job after the tournament in Brazil, said the process of signing for Manchester United had been relatively quick.
It didnt take very long. I was approached directly after the sacking of (David) Moyes. I have negotiated much longer with other clubs.
He said he had already had intensive discussions with his new club over his coaching staff, the playing squad, the pre-season preparations and the youth development set-up at the club.
I have no agent but I had a friend who is a specialist in negotiating to do the deal for me. If you negotiate yourself it affects your relationship with those seeking to appoint you and I dont think thats a good idea.
Van Gaal said he had sent a text message to family and friends 30 minutes before Mondays announcement, including one to Chelsea manager Jose Mourinho, his former assistant in Spain.
He was the first who responded. He said he was jealous of the list of clubs that I have worked at, said Van Gaal, who first coached Ajax Amsterdam and has worked at Barcelona twice, Bayern Munich and won the Dutch title with unfashionable AZ Alkmaar in 2009.