I think he ment flipping them over..
What i do is :
1. Get a new transperant file, not layer, a new file.
2. But the brush on there.
3. Go to "Image" and then flip it horizontaly, verticly, or with a custom degree.
4. Once done, select the image ( ctrl + A since the background is transperant ) and then paste it where needed (ctr+v).