I am a Shakta Hindu.
I believe Shiva-Shakti are one; Shiva is the transcendent, unchanging aspect of God, while Shakti is the immanent aspect that is the prime mover of the universe. Shiva-Shakti is the same as Brahman.
I believe Shakti manifests herself in innumerable ways. She is all the Hindu gods and goddesses and all the gods and goddesses of all the other religions as well. I think the reason for the many manifestations is to appeal to all people. She's the same Shakti, just wearing different hats, so she looks different.
The manifestations I personally worship are the Hindu gods/goddesses Durga, Kali, Lakshmi, Saraswati, Ganesha, and Shiva and the Greek goddesses Aphrodite, Athena, and Hera. To me, these are all aspects of the one Shakti.
I believe that Shakti does descend occasionally as various avatars.
I believe in karma and reincarnation. I think there are both heavenly and hellish realms that a soul can go to after death, but I don't believe they're permanent. You only stay there for as long as you need to work off any karma incurred in past lives. Ultimately, we all return to Shakti in the end. Each individual soul is a piece of her.
I'm sure there's lots more that's relevant, but that's all I can think of right now!