Navigate to the page you wish to modify

Click on Edit.

Click on the  sign below the title box.  This prompt will also appear between any existing web parts.   

Select Document Library from the dropdown list of web parts.

Select the document library you want to add to the page.

Click Edit web part button on the left side to configure the web part

The Document Library window appears to the right of the screen.

Select any available library view and folder.

Select the required size of the web part.

Click Apply.

Select Publish (or Republish) at the top right of your page to make the changes visible.