(Non-)aspiration describes whether a out-breath is made during the sound production:
- Aspirated means there is an audible out-breath.
- Non-aspirated means there is no out-breath whatsoever.
So basically you have to breath-out when making the sound (for the aspirated consonants)
The best method to practice the pronunciation is to hold your hand 5 cm (2 inches) in front of your mouth and just feel whether there is a breath coming out when making the actual sound.
This matrix explains how all T and D sounds fit into one system of sound production:
Practice saying these words:
होटेल (hoTel) – Hotel
उठ्नु (uThnuu) – to get up
तिमी (timii) – you
अर्थ (artha) – meaning
माड्नु (maaDnuu) – to massage
ढिलो (Dhilo) – late
सधैं (sadhai~) – always
दुर्इ (duuii) – two