HR managers tell us that their company has a friendly environment, and that teamwork and honesty are appreciated. So you get the impression that everyone is your best friend. Don't believe it.
We all tend to compete with each other, and it would be just naive to pretend otherwise. There's nothing wrong with that. Just don't treat your coworkers like friends, don't expect too much from them. People actually work to get money for their job. It would be a mistake to think that they can sacrifice their salary for the sake of friendship. Base your relationship on a different model.
Be friendly, have fun with your colleagues, but above all remain professional.