Dental vs. Alveolar Consonants
In Latvian the sounds represented by the letters t, d, s, z, n, and l have a dental pronunciation. That is, they are said with the tip of the tongue at the upper teeth. In English, the corresponding sounds are alveolar. That is, they are normally said with the tongue at the alveolar ridge, which is the bony ridge running across the roof of your mouth, just behind your upper teeth.
The following diagrams show the lips, upper teeth, roof of the mouth, and front part of the tongue in cross section (as if you were looking, from the side, at an X-ray that showed a head facing to your left). They illustrate the difference between the positions of the tongue when producing these two types of sounds: