The Faces data type contains six booleans representing whether a feature is enabled for each face (enum/NormalId) of a Part. In other words, this contains a boolean for each axes (X/Y/Z) in both directions (positive/negative). The Handles object uses this data type to enable whether a direction has a visible handle on a Part’s face.

local handles = Instance.new("Handles")
handles.Faces = Faces.new(Enum.NormalId.Front, Enum.NormalId.Left)

Like most data types on Roblox, the Faces data type is immutable: you cannot assign to its properties once created.