BRICS and its Mechanics?

What exactly is the multi-lateral BRIC(S) framework and towards what benefits is/was this organized. Against what criteria was South Africa (new member) inducted within the BRICS framework ? IN what Currency denomination is Credit extension and settlement planned between the BRICS, hence the composition of trade inter- and intra- BRICS.Where can one find the Combination[5C2] Cross-rates of currency pairs of BRICS and what is the designated reference benchmark currency/value ?