"Voy a la tienda" is "I am going to the store" in Spanish.
"Bookstore" in Spanish is "librerÃa". It is pronounced "lee-brare-EE-ah". Please see this site for confirmation of the translation: http://www.answers.com/library/Translations
You can say "En la tienda".
Tienda de articulos usados, or tienda de articulos de segunda mano, are "Second Hand Stores".
When you want to say toy store in Spanish, the word is jugueterÃa