but IDK how to use it
Then I guess you haven't implemented it!
Well, that method will convert a file of yours (saved at SD card, eg) to a resized Bitmap wich can be used as background of an ImageView.
Now, answering to your question, you can use it as I show you below:
Bitmap bitmap = decodeFile(new File(your_string_file_path));
myImageView.setImageBitmap(bitmap);
That's all you have to know, I guess.
