The revenue insight provides an overview of the gross revenue generated by your business in the given time period. This is represented as a trending line graph. In addition to the gross revenue, this insight also provides an overview of your overall PayPal account and financial health of your business by showcasing other metrics like net revenue, fees charged by PayPal, total refunds paid out in the given period as well as average revenue / sale. These metrics give you a high level view of your business's financial state.
If you find big spikes in revenue, look at what caused that spike, maybe it was a marketing newsletter announcing a new product to your regular customers, or a social media post to your Facebook fans. Knowing which sources lead to more conversion and sales will help you focus your efforts on them for higher returns.