Click in the document where you want to insert your graph. For example clicking below a paragraph of text will set that location as the place to insert your graph. Create your equation select it all copy switch to Prism and paste.
The add-in also provides an extensive collection of mathematical symbols and structures to display clearly formatted mathematical expressions.
This tab is on the ribbon menu just below the highest row of icons. This produces very nice complex graphs. That adds r squared to the graph just below the equation as in the snapshot below. Go to Insert tab find Symbols group and click Equation button.