the sun - Does the sun itself present the problem of global warming is it the main cause?

The energy input of the Sun stays constant (mostly, there are some minor variations), so no, the Sun is not responsible for climate changes.

The temperature of the Earth has to do with the balance between the energy input, and the energy radiated back into space. If the temperature is not changing, they are the same.
Global warming is caused by gasses in the atmosphere limiting the energy radiated into space, therefore, the temperature rises, until the energy radiated is again equal to the solar energy input.