Buttons are used to initialise an action. Button labels express what action will occur when the user interacts with it.
Primary button have the highest emphasis as they have a color fill, they are used for the most compulsory actions and do a good job at grabbing attention. They are used for primary or high emphasis actions.
Can also be used along with other Secondary buttons or ghost buttons.
The secondary button is for medium emphasis. It is meant to be paired with other button types to surface less prominent actions. It can be displayed in visible stroke. Secondary buttons are paired with icon.