Tamarind is a sour fruit that is used in Thai recipes to add a sour note to balance a sweet flavour. The easiest way to buy tamarind is in packets as a pulp, in that form it looks similar to pulped dates. The tamarind pulp itself isn't usually used, rather tamarind water is used.

Preparation for Tamarind Water
Take a piece of tamarind pulp, approximately 100gms. Soak the pulp in water for 10-20 minutes. Squeeze the tamarind pulp with your hand to squeeze out the sour juices. Use the water and keep the pulp in the fridge to reuse. You can reuse the pulp several times until it loses it sourness.