Difference between IFormEncoder and MHttpDataSupplier in Post method

I want to post two values to server from my Symbian Application. 1) To send data, I tried to use iFormEncoder....My doubt is, what is the use of MHttpDatasupplier and its methods...Shall i want to use these datasupplier methods while using iFormEncoder....

2) In MHtpDatasupplier, How to use GetNextDataPart and ReleaseData methods...In that methods many tutorials used, iPostData and iDatapart...what these are...How to match these with my iFormEncoder data....These are confusing lot....please help me....