通过触摸或点击在Android Google地图上添加标记

I am a beginner in Android Developer. I want to develop a Map Application using Google Map. Now, I want to add marker on the map via Touch or Tap on the Map. I do not know how to apply touch event to drop the marker on the map. Please tell me and, if it is possible, please give me some links or examples. Thank you and sorry for my English.I am a beginner in Android Developer. I want to