Does anyone know what would be the exact or approximate altitude for the stage separation and spacecraft separation of LEO insertion? Moreover, does anyone has a picture including all step of LEO insertion? Thank you very much :)
What you want to search for to get this information is 'launch sequence'. It depends on the rocket and the payload. What happens up to first stage separation is pretty standard, what happens with second stages is more variable.
If the rocket has boosters (the thin cylinders that are strapped onto the sides), they will separate between 30 to 60 kilometers altitude depending on what rocket it is and its configuration. With or without boosters, the first stage will separate at 100 to 130 km, again depending on what rocket it is. For the most part, what the first stage does is get the vehicle out of the atmosphere.
The second stage gets the vehicle up to orbital speed. Therefore what it does exactly depends a lot on what the payload is. On some rockets and with some payloads, once it has done that it's job is over and it separates. In other cases it burns twice, once to get up to orbital speed, and again on the opposite side of its orbit to raise orbital height and make it circular. What height that is depends on the payload. Then it is discarded.