Using Custom Field Sets
Field Sets allow you to select a group of fields from an object and those related to it. They are used in apps to determine which fields should be displayed on a custom page, as well as which fields need to be required.
You can specify a custom Field Set to be used in place of the one included in the package, which will allow you to choose fields from a wider selection, including those from other managed packages. It also enables you to create separate buttons for each field set and place them on different page layouts.
Creating a new Field Set
Creating the Custom Button
Navigate to the Field Set page for the object you plan to add a Field Set for and click New.
Give the new Field Set a Label, Name, and "Where is this used?" to help distinguish it from existing Field Sets. Once entered, click Save to continue.
Find the fields you would like to include in the Field Set and drag them into the "In the Field Set" section. You can select fields from the object the set belongs to and also fields from any object that is linked to the main object via a lookup or master detail relationship.
Once a field is added you can make it required by hovering over it and clicking the wrench icon. Then, check the box under Required and click OK to continue. You can also remove a field from the set by hovering over it and clicking the minus icon.
Once you have selected all the necessary fields and set the appropriate ones as required, click Save to finish the Field Set creation.
Clone the button you would like to use a custom Field Set with.
Clone the existing managed button and update the URL included in it by the adding the URL parameter "fieldset" followed by the Name of the new Field Set, for example &fieldset=Custom_Field_Set. If an invalid Field Set Name is used, the default set included in the package will be used instead.
Add the new custom button to the appropriate page layouts.