Well for Mobil you press the browse icon in the bottom left corner of your screen and tap the question you wanna answer and press "answer this question" at the bottom and type your answer and then press "post answer"! Good luck! :)
I'll only tell you if you tell me how to ask a question! Haha jk. Click on a question and there should be a text box at the bottom of the page with he words 'Do you have an answer?' above it. Just start typing in that box and when you're done, click the Submit answer button and you're all done! Remember that if you write something inappropriate, it'll be removed by moderators!