The time taken for the main content on the web page to appear to the viewer is the largest contentful paint. Benchmark of LCP: It should be < 2.5s.
FID measures the response time of your web page when a user interacts with it for the first time. Benchmark for FID: It should be < 100ms..
CLS is the measure of sudden layout shifts of your webpage which hampers the overall user experience. Benchmark: It should be < 0.1s.