Hi Swetha,
Have a look at this article and see if that clarifies:
https://community.marketo.com/MarketoArticle?id=kA050000000L59HCAS#
I pasted here a couple of paragraphs:
Acquisition-related measures are labeled FT, for first-touch attribution. Acquisition-related measures give credit to the program through which a lead’s contact information – especially the all-important email address – are first obtained
Success-related measures are labeled MT, for . Success-related measures give credit to all the programs which contribute to a lead’s progress toward a purchase. Using multi-touch attribution reflects the cumulative nature of sales success. A lead does have to achieve success in a program for success credit to be awarded.
This other article is a lot longer but it goes into specifics on how it works.
https://community.marketo.com/MarketoTutorial?id=kA250000000KyvhCAC#