To start go to the 3 lines menu in the top right hand corner and choose 'School settings'.
Then choose 'Custom fields' from the left hand side of the page and then 'Custom fieldsets'.
Click 'Add fieldset', and then give your fieldset a name
You will then be presented with the second stage of the fieldset process, where you are able to choose which fields to use. Each fieldset must contain the fields selected by default, but you can select the rest that are visible (up to four or eight per side (including defaults) depending on school settings).
After you have chosen your fields, click on the "assign lessons" button.
On this screen, you can select the lessons that you wish to apply the fieldset to. You can search for the lessons manually using the search box (1), filter the results by a subject (2), or by selecting all lessons using the checkboxes (3).
After clicking the "save and return" button (4), this fieldset will now be forced on all the classes selected.