Isvara
Both nirguna brahman and Isvara are accepted and worshipped. Entire world is the play or lila of Isvara. And Isvara hence could be worshipped as sakara. This can also be understood in the light that Viśiṣṭādvaita is religion + philosophy. Both upasana and Vedānta are closely knit.
The eternal is said to be five-fold, and worshipped in these five forms:
Para - The eternal being. This is Sri Maha Vishnu in times of non-creation in Vaikuntha, sleeping in the coils of infinity.
Vyuha - The one with four aspects, Sankarshana, Vasudeva, Pradyumna and Aniruddha (Vishnu Shasranama praises Him as caturvyuha, or having four vyuhas).
Antaryamin - The One (as soul) that pervades all creation.
Vibhava - The glorious incarnations of God, such as Sri Rama and Sri Krishna.
Arca - The forms of worship, such as incarnations, idols. Example of Arca-avatara is Venkateswara.
Jiva
Jiva (individual soul) is said to be anu (indivisible),avyakta (unmanifest), acintya (unthinkable), nirvikara (having no distortion or transformation) and jnanasraya (the abode of knowledge). Jiva is an indivisible part of Isvara.
There are three types of Jivas, bound, liberated and eternal. Any Jiva prior to liberation or moksha is said to be bound. Post liberation the Jiva is mukta, and merges in Isvara. There are eternal jivas too, that are not bound but exist - such as devatas, consorts, servants, vehicles of Vishnu (Garuda, Java-Vijaya etc).
Prakriti
Prakriti is the cause of manifestation. It causes the three consiousness qualities, satva, rajas and tamas. There are two forms of satva, suddha satva and misra satva. Suddha satva is one that is not touched by rajas and tamas - this is the one that manifests in Vaikuntha, creating the "eternal" beings like Garuda and Anata. This is said to be nitya vibhuti. The phenomenal world is caused by misra satva, a combination of all the three qualities. This is said to be lila vibhuti.
-India Mythology (Short Info).
