What is the difference between Exchange & Offer in the Monetary System for NXT / Ardor Platform? When creating a new monetary system coin on the NXT/Ardor platform. What is the difference from Exchange and Offer? 

What does the following mean in the Exchange Window?


Minimum Rate
Effective Rate


What do the following mean in the Offer window?


Buy units (Initial) 
Buy units (Limit) 
Buy Rate per unit 
Sell units (Initial) 
Sell units (Limit) 
Sell Rate per unit
Please refer to the official monetary system documentation https://bitbucket.org/JeanLucPicard/nxt/issues/205/monetary-system-documenation section "Currency Exchange".
The NXT wiki also has an excellent walk-through of the process in https://nxtwiki.org/wiki/Monetary_System#Exchange_an_Exchangeable_Currency