How could I play guitar chords without it buzzing?

I do press my chords tightly, and I do hold my fingers behind the frets and not directly on them. Sometimes it doesn’t, but sometimes it does. Like when I play a chord where a finger has to cover more than one string.

Thanks.

P.S. My guitar is new, but in tune.

You’re putting fingers on the frets??? There’s your problem. The finger should be just behind the fret but right against the back of the fret, never on top of the fret. Good luck.