Android and wordpress API

Hello,

i have a wordpress based website for questions and answers, you register to ask a question (add a post) and answer it (add comment), so i was trying to hire an android developer to develop an app for the website that helps people register, ask and answer through the app directly but almost all of them asked me the same question regarding wordpress API to hook the app to it, so not sure where can i find an information like that? ??

if anyone could shed any light regarding this matter it would be much appreciated

Thanks in advance