What you need to know:
You will soon be able to use text formatting (bold, italics, and underline) in Forms surveys and quizzes differentiate and emphasise content.
What you need to do:
Nothing, this update will rollout automatically. Your experience will be consistent with other Office 365 products, you will be able to format text by using either a floating tool bar or keyboard shortcuts.
In the editing canvas of the form, you will can also use the text format toolbar inline whenever they are composing text content:
Availability:
This rollout has already started and should be complete by early-February in March (a little later for government customers).