Can someone tell me how xirr is calculated

I don’t understand XIRR. I started a SIP 2 years ago, and the XIRR stands at around 30%. The problem is, how do I compare it? For a lump sum investment, if my absolute return is 50%, that means 25% per year, which is more than double the FD rates. But how do I compare XIRR returns to FD rates? How can I know if I’m beating FD rates? I also made a lump sum investment where the absolute return shows a 1-2% loss, but the XIRR for that investment shows an 11% loss. I’m confused. How do I interpret this?