,Problem with Unity Android unity 5

Hi
sorry i can’t speak english very good…
I use Google Transcend
Unity version 5.6.6f2
32bit
I’m a beginner at Unity.
When i want to choose the sdk files, But I can not.
Where is the problem? Please help me…

probably you didnt downloaded android tools while installing unity, go to Edit->Build Settings->Click on android-> Download