ms-Button

<button id="ID_button" class="ms-Button"> 
   <span id="ID_label" class="ms-Button-label">label text</span> 
   <span id="ID_description" class="ms-Button-description">description text</span> 
</button> 

Primary Button

<button class="ms-Button--primary"> 

Command Button

Includes an icon

<button class="ms-Button--command"> 

Compound Button

Includes an extra descriptive line below

<button class="ms-Button--compound"> 

Hero Button

<button class="ms-Button--hero"> 

aria-hidden

This attribute prevents screen readers from reading the icon.
If you are using an icon-only navigation bar, you should apply an aria-label to the button