T and D are both "dental consonants" (they involve pressing the tongue against the back of the upper teeth). The difference is that D is "voiced" (vocal chords vibrate)' but T is "unvoiced" (a simple burst of air with no vibration of the vocal chords). C and G can also be considered a voiced/ unvoiced pair. Practice these sounds while gently holding your hand to your throat. You sound feel a vibration when pronouncing D and G (and no vibration when pronouncing T and C). Also, if you hold your hand in front of your mouth, you should feel a stronger burst of air for T and C than for D and G. Once you have spent some time properly producing these sounds, hearing the difference should be much easier.

gateau le son "ga"se fait au fond de la gorge et "teau" sur le devant de la bouche cadeau le son "ca" se fait sur le palet et "deau" sur le devant de la bouche