Either go direct to this link: Schema Builder

Or click on "plinth" in the top left corner and scroll down to "Settings", where you can add/edit fields:

Click on "Fields" and then "Add/Edit Fields". This will take you to a screen like this, which will show you the fields you already have in the database:

They are split into "Details Fields" and "Reporting Fields". Details Fields store information that you are interested to know about a person, such as Telephone Number or Emergency Contact. Reporting Fields are those that you might want to do analysis on, such as Ethnicity or Gender.

On the left-hand side are listed the different types of fields that you might want to add. To add a new field, select the field type and then drag and drop it in. By default, it will show you a blank field like this:

The field name is the name that will be associated with the field, for example, School. If you type that into the box it will show up alongside the other fields.

If you select a field type such as "Dropdown: single choice" or "Dropdown: multi choice", you will be given the option to add options for this. These will then be the options shown on a Member's profile or on any forms that have that field included. You can edit fields already there by clicking on them from the list.

Here, you can also make your field a reporting field (e.g. Gender, date of birth), where you can gather information on this in the reporting tab.

Once you are happy, click "Save Fields" in the top right corner and you are done!