Tamarind fruit comes in seed pods that look like big castor beans. They're kind of like dates, I would think (I don't eat dates, so not sure, taste-wise.)
When I want to use it for something, I buy a puree or paste of it in frozen concentrated form at the grocery. I've had a drink of it in Mexico and in the Caribbean, which is why I think they have this concentrate here in Houston.
I really never thought of it being in Worcestershire sauce until you brought it up! And I can drink W'shire by the gallon, lol.