Aquí and acá, are the same thing (it's here) allí, allá, and ahí, also are the same thing (it means there) Saludos desde Venezuela mi pana ;)

I agree with the reply of Raúl. And I add: As a Spanish, "Acá" and "allá" are not often used in my country. They are mostly used in Latin America. But I remember we have an idiom which uses "allá" and says: "Ir de aquí para allá". It means to move constantly. Eg: Ayer estuvimos de aquí para allá toda la mañana (Yesterday we went to many places all morning: supermarket, hairdresser's, post office, etc). Except this one, you won't hear "acá" and "allá" from Spanish people. All the best! :)