This article will go into detail on the Generated fees tab of our Uniswap V3 position page. For a more broad overview of supplying liquidity with Uni V3 see our walkthrough here: https://blog.apy.vision/how-to-provide-liquidity-to-uniswap-v3-on-polygon/
The goal of the Generated fees tab is to give you a detailed breakdown of the trade fees your Uniswap V3 position is (or isn't ?) generating. Remember, V3 positions only generate fees when they are in range.
There are 2 main data windows at the top, Previously collected fees and Pending fees. The Previously collected fees are calculated by multiplying the amount of tokens received at the time of your claim by the token price at the time of claim. So this value is "fixed" and won't change as the token prices shift up or down after your claim. Would you like a toggle to be able to see your previously collected fees at current prices or at price at time of collection? This should be a future feature. If you would like to see it let us know on twitter, discord, etc and you can help us to prioritize that. The Pending fees are shown at current market values since we know you haven't sold those yet.
In the chart below the two fees boxes you'll see a blue line that represents the value of your Previously collected fees + Pending fees. Generally this chart should trend upwards, but it can go down if the USD value of your Generated fees goes down. Remember, the Pending fees part of the equation is ever changing based on current market values while the Previously collected fees are fixed at a particular value. So this chart may look more volatile with more pending fees than collected fees.
At the bottom of the chart you'll see a visual representation of the fees earned each day as gray bars. You can hover over the chart to see the values for Fees generated per day and Cumulative fees.
You will notice that if your position goes out of range for a period of time you will see no gray bars because the position isn't generating any fees.
Expanding the "View daily fees breakdown" button you will see a table of fees generated each day since the inception of the position. The daily fees use a price from the end of the day UTC time which then doesn't change in the table. The Cumulative fees value equals the value if you sold your fee tokens for USD at the end of each day. So don't be surprised if that Cumulative fees value differs from your Generated fees figure.
The next section below that is all about your Previously collected fees. It shows the amount of each token you have collected to date as well as the average price of all of those collections. Below that area you'll see the actual collections including the amount of token, the price of the token at that time, and the product of those two values which gives you the total USD value of that collection. At the bottom you'll see those values summed up for a total value at time of collection for each token. The sum of those is displayed and should equal the Previously collected fees number on the top of the page. 
At the very bottom of the page is a similar breakdown for your pending fees. These token values are shown at the current token price. You'll notice that the sum of these values is what makes up your Pending fees at the top of the page.
With this info you should have a solid understanding of the fees you are generating with your Uniswap V3 position and how much those fees are worth. It is easy to go back and see time periods where you were out of range and not generating any fees and you can see various trends related to your generated fees.