I think enoilgam's response is sufficient for a high level explanation on how the RBA executes monetary policy and either purchases/sells securities to increase or decrease the supply (or availability) of cash. That being said, as evidenced by big banks no longer following the RBA cycle in interest rates, this is having less and less of an impact on lending activity compared to a decade ago.
To answer your second question osak23, I am not really sure to be honest. The challenge in answering your question is whether you mean broadly moving from private to public, or in an Australian specific context where private (i.e. proprietary) companies fall into two categories depending on various financial and non-financial criteria. Can you be more specific in your question? I'd need to search on ASIC but I presume there are fees involved as ASIC do charge fees when lodging forms.