CEDAW and the Beijing Platform for Action are similar in that they are both international agreements made by governments about women’s human rights.
However, CEDAW is more like a policy document or a law, which clearly sets out what women’s human rights are. It is legally binding under international law.
The BPFA on the other hand sets out in more detail, what sorts of actions governments have to take to put into practice the human rights identified in CEDAW. It is more an action document. It is not legally binding-governments have a strong moral obligation rather than a legal obligation to act on the BPFA.
The strongest position women’s groups have is to work on both processes so that governments put into place both policy and actions for achieving women’s human rights.