The Dm7 guitar chord is the start of barre chords. Barring chords is when we hold down more than one string with one finger. In most cases that’s done with the index finger.
This one is a good started barre chord as it only requires two strings to be held down. Other barre chords require 5 or 6 strings.
Press firmly with your barre finger and bring your thumb further around the neck to squeeze the pressure into your barre finger. Effectively “pinching” the neck.