Difference b/w TOF, MOF,BOF Ads content?

I see some people talking about creating three layers of ads TOF, MOF,BOF. How do these ads differ in their content?

If there's a product (without discounting) let's say a trimmer. How does the content of top of the funnel, middle and bottom differ? (P.S. all the ads will be running for purchase itself but content will differ but how?)