You can find the text of the MLI here. The Explanatory Statement, also at that link, is so far only in English.
Three months after five countries ratify, the MLI will be in effect; subsequent accessions will take effect one month after ratification. However, as to optional provisions, no substantive changes take effect until both parties notify which provisions they intend to apply to which of their treaties.
The OECD has designed three types of provisions and explains how they relate to existing tax treaties. Here are my notes to self:
Much more analysis to do obviously, but my first cut at this is to try to understand the process of integrating the MLI into the existing tax law order.