Apsaras are usually in the Swarga Loka and Indra is the King of the Swarga. But, this Swarga is not considered as the final place of Moksha or liberation. Swarga Loka also has its own cycle and it undergoes dissolution in the Naimitik and higher Pralayas (destruction).
As Satsangi has mentioned, these Apsaras are there in the heaven and are for the entertainment of the Devas. Concept of Heaven is different from Abrahmic religion as it is just a temporary stage. One's soul may go to heaven after dying just because he/she desired or due to the fruits of one's Karma. But the "self" should remember that this is not the final stage and it is just a materialistic reward for one's Karma which is not forever and is temporary. Only Moksha that brings eternal bliss with the union of GOD is true liberation.
Apsaras are usually in the Swarga Loka and Indra is the King of the Swarga. But, this Swarga is not considered as the final place of Moksha or liberation. Swarga Loka also has its own cycle and it undergoes dissolution in the Naimitik and higher Pralayas (destruction).