1. Images should for profiles should be 100x100 pixels size. We need to adjust both Image Canvas and Size to get the 100x100 result. Open photo in Photoshop and crop an approximate square by selecting the area and then going to Menu>Image>Crop or using corresponding tool. To make it a perfect square go to Menu>Image>Canvas Size and make width and height equal to each other, check the Image and then move to Menu>Image>Image Size, here you can change the size to 100x100 pixels.
2. Other pictures are recommended to be saved in 350x262 pixels format.
3. After cutting and cropping go to File>Save for Web and click "Save".