What is Brahma?

Brahma is Totality. It is the source of all existence. Brahma is ultimate reality existing as complete oneness, beyond any idea of separateness.

Brahma is beyond Purusha and Prakriti. It simply is.

सर्वँ् ह्येतद् ब्रह्मयमात्मा ब्रह्म  

 sarvam hyetad brahmayamatma brahma

 "And everything that is, is Brahma. The Atma(Self) is Brahma."

Can I experience Brahma? 

The aim of yoga is the expansion of the individual consciousness to the level of Brahma. The individual experience of Brahma is called Atma. In the process of yoga, we become free from the limitations of individuality and acquire the status of Atma or Brahma. This experience is called Ananda.

ब्रह्म्असंस्पर्शमत्यन्तं सुखम् । 

brahma samsparsham atyantam Sukham

"Contact with Brahma is infinite joy."

-Bhagavad Gita 6.28