The 2010 finalists have a tough job on their hands to progress to the knockout stages of the competition after being drawn alongside world champions Spain, Chile and Australia in Group B.
Netherlands’ rearguard has been criticised as the team’s weak link despite Louis van Gaal’s side winning two and drawing one of their three friendlies ahead of the tournament.
And while Vlaar admits the attacking line-up of Robin van Persie, Arjen Robben and Wesley Sneijder are the side’s best assets, the 29-year-old says they are working hard to improve at the back.
When asked whether the defence was the team's weakness, Vlaar said: "We know that. We work hard to get better as a team and we also know we have our best players up front.
“But if you look at all the games we played during qualification and friendlies, we didn't concede many goals.
"So we have to give confidence to our forwards to accelerate and make a difference for us.
“You play every game to win. You have to be realistic but I really believe we can achieve something. I look forward to it and I cannot wait."
The Oranje have suffered heartache in the World Cup before, having lost three finals in the past – most recently against Spain in 2010.
Van Gaal claimed earlier this week that his side were expected to reach the semi-finals in Brazil at the very least.
And Vlaar backed up the target set by his coach, stating that Holland could even go on to win the tournament - but only if the players performed at their very best in Brazil.
"You have to believe otherwise you shouldn't go."