The basic tenets of Sanatan Dharma are a common thread that hold together a diverse history of experience and belief on the Indian subcontinent. These tenets are karma, reincarnation and the existence of Parmaatma.
Bhagwan is one. All prayers end up in one place, regardless of how they got there: through the chanting of the "Aum" mantra or through devotional bhajan or through nishkaam-karma yog (selfless service) or through the various modes described in the vast body of scriptures.
The tolerance of different paths to the one, ultimate Truth is a cornerstone of practice in Sanatan Dharma. It's the reason you see the idols of different deities side by side under the same roof! For some, like the adherants of Vedanta, the path to Parmaatma is not through idol worship at all; again, this is a valid and recommended path by the Vedas and Upanishads.
When asked about Bhagwan, we'll often answer with attributes extolled in scriptures: all-merciful, gracious, all-powerful and may more. Yes, Bhagwan is all that but He is a lot more. In fact, Bhagwan is just as equally Him, Her and It, and Bhagwan is a lot bigger than the human mind can ever perceive. If your prayer is sincere, Bhagwan will use whatever form of the divine you worship to guide you to Her.
"Paramaatma" is the Sanskrit word for "primary" (param) "soul" (aatma). All living beings in this and all other universes are part of the Parmaatma. Sanatan Dharma teaches us that all of existence is a single cosmic energy. Following that, we can say that all souls are related to each other and have taken a temporary break from the Parmaatma. Eventually, we'll all merge into the Parmaatma. In Dharmic philosophy, all phenomena are described through the metaphor of cycles. Merging into and breaking away from Parmaatma are the epitome of such prose and poetry.
From this basic understanding of Parmaatma comes the realisation that since all beings are interconnected, violence against one being is violence against us all.
This belief of the interconnectedness of all living beings has translated into a culture of tolerance and has meant that the Indian subcontinent has been a long-standing, vibrant mosaic of diverse cultures. Certainly, periods of intolerance can be cited but tolerance has been the norm over the course of history. Scholars peg the following numbers to describe diversity on the Subcontinent: 80,000 subcultures; more than 325 languages, resulting in thousands of dialects; 25 commonly used writing scripts.
All of existence is a single cosmic energy. Each soul is a part of Parmaatma and is on a kind of tour of duty in the material world. In the Bhagvad Gita, Krishn Bhagwaan talks of the atman - the individual soul on the tour of duty - passing through physical bodies as though it is wearing and shedding clothes.
After a body dies, the atman leaves it, continues on a cycle that includes after-death experiences and enters a new body that befits the atman's Sanchita (accumulated) karma.
Reincarnation is a difficult concept to accept sometimes, especially in an age of material science where people demand empirical evidence. Fortunately, the case of Shanti Devi in 1930s Delhi provides documented proof of reincarnation.
Until the age of four, Shanti Devi spoke very little and when she did, everyone around her was shocked. She would say that her Delhi home was not her real home and that she must return to Mathura... to her husband and her son! Shanti Devi continued to tell anyone who would listen about her 'real' home. One such person, her teacher, sent a letter to the Mathura address given by Shanti Devi. To the teacher's surprise, a reply came back from a man stating that his wife, Lugdi Devi, had passed away some years earlier, after giving birth to their son. The details that Shanti Devi provided about her old house and family members were all confirmed, launching the most thoroughly researched investigation of a case in reincarnation in modern history. Sture Lönnerstrand's 1998 book, "I Have Lived Before: The True story of the Reincarnation of Shanti Devi", is considered by some to be the definitive account of Shanti Devi's story.
"Karma" is the Sanskrit word stemming from the Sanskrit root "Kri", which means "to do".
If the aatman is a travelling vehicle, then karma is the engine which drives it. Dharmic scriptures describe three types of karma: Sanchita, Praarabdh and Kriyaaman.
Sanchita karma is the accumulated karma of the aatman's entire cosmic existence. During the present life, a small portion of Sanchita karma bears fruit and is exhausted. When all Sanchita karma is exhausted - through cycles of birth and death in physical bodies - the aatman merges with Parmaatma.
Praarabdh karma is the portion of Sanchita karma that ripens in the aatman's current incarnation. Working through this current portion allows for stocked-up karma to be released for future incarnations.
Kriyaaman karma is created in the present lifetime; you could call it instant karma. Some of this Kriyaaman karma - or Aarabdh (commenced) karma - is experienced and exhausted immediately, e.g., being cited and convicted of a parking fine and subsequently paying off that fine. The rest of Kriyaaman karma - or Anaarabdh (not commenced) karma - is stored with the aatman for future-birth experience and exhaustion.
Numerous questions may arise from understanding the basics of karma. Sanatan Dharma encourages you to ask questions in a critical manner so that you may recognise your true self, your aatman. Once you recognise your aatman, you can proceed to work through Praarabdh karma. Seeking the guidance of a guru is paramount in this endeavour, much like seeking the guidance of mathematics teacher when learning algebra or trigonometry. A true guru will guide you on a path that nullifies the effects of Sanchita, Praarabdh and Kriyaaman karma; this, in turn, will free your aatman from the cycle of birth and rebirth, merging it into Parmaatma.