how to develop a basic online ordering app? : need a small clarity regarding developing an android app..basically the idea is to build an app where the user can select the items(eg.books),after selecting he will be taken to next activity where he can choose the number of items(say 2)...after selecting he will be taken to another activity where he is given option to pay online.After payment..the seller(that is me)should generate a bill containing the details provided by the user...so my doubt is...how to know what items has he selected and the details(how do i receive that info) he had entered and how do i generate a bill back to him?....please help me with this...i just need an idea of how to implement it...thank you!