To do this go into one of your classes.
In the bottom right hand corner of you class you will see the custom fields legend which will normally display the default fields your school has chosen.
Click on the 'Choose fields' button.
The drop down menu above the field sets will display 'Use default fields'. Click this and change it to 'Use custom fields'. You can also choose a specific custom fieldset which the school admin has created.
Some fields will be greyed out and this means they must be shown on your pupil cards as default. You are then free to tick what fields are shown on your cards (4 or 8 per side depending on school settings). If you tick the visible column the fields will display on the front of your cards, if you choose flip they will appear on the reverse of your pupil cards (if flip is enabled in school settings).
As you tick the boxes, you will see a preview of what your pupil cards will look like with these fields included on the right hand side of the screen.
Once you have finished, you can return to your class by clicking the 'Return to class' button in the top right corner of the screen.
The class legend will now display the custom fields you ticked, and their attached information will be shown on the pupil cards.