The Bio Tab is where you can store basic details about your users and upload an image or avatar. This may be useful if the user concerned is also a contributor, as this information will be linked to their contributor information.
The image below shows the relevant dialogue box, in which you need to manually type (or cut and paste from a word document) the biographical details.
If you want to add a photograph of the user, you can do so by clicking on Choose File from within the Image field, as below. This will take you to your computer files where you can pull the image in from.
Click on Update to save the information.