You go to your post for item for sale. Click edit then you can go into the body of your post and add in the info required. I believe you have to go to advanced to change the title to WTS. In the post body you can insert your location and another email address for contact. Also under advanced is where you click on manage attachments to add pictures.
I am not up on Android use so I don't know to comment if your problem is with your phone. I believe your problem is from not clicking on advanced to make your changes.
Also go to Introductions and there you can leave your info so other member can know who you are and your interests.
If this doesn't help then let me know.