There are two types of meditations described as "Samatha" and "Vipassana" I have heard that there are several types of samatha bhawana (40 kamatahan). Can you please elaborate this based on Theravada Buddhism
As answered here, the forty samatha meditation objects are:
1-10: The Kasinas
These all lead to the four jhānas; they are practised by creating a disk and focusing on it, while repeating, e.g., "earth, earth..."
These lead to the first jhāna; they are practised by contemplating a corpse in various states of decay
14. Cut Up
15. The Gnawed
17. Hacked and Scattered
20. a Skeleton
Body and Breathing bring jhāna (body only brings the first jhāna, breath brings all four); the other eight bring only access concentration; they are cultivated by reflecting on the object, e.g. "Buddha, Buddha"
31-34: The Divine Abidings
The first three bring about the first three jhānas; the fourth brings about the fourth jhāna; they are cultivated by taking beings as an object, e.g. "May all beings be happy"
35-38: The Immaterial States
These bring about the fourth jhāna; they are cultivated by using the fourth jhāna as a base, then expanding and refining the object
35. Limitless Space
36. Limitless Consciousness
38. Neither Perception Nor Non-perception
39. Perception of Repulsiveness in Nutriment
This brings about only access concentration; it is practiced by reflecting on food as one collects and eats it.
40. Defining of The Elements
This brings about only access concentration; it is practiced by breaking the body up into the four elements.
All forty meditation subjects are described and taught in detail in the Visuddhimagga; highly recommended for those interested.