At the core, this formula extracts characters from the right with the RIGHT function, using FIND and LEN to figure out how many characters to extract. C4 contains the text "email@example.com", so LEN returns 17 characters:
LEN(C4) // returns 17
FIND locates the "@" character inside the email address "firstname.lastname@example.org". The "@" character is the 7th character, so FIND returns 7:
FIND("@",C4) // returns 7
The number 7 is then subtracted from the 17, which is 10. The number 10 is used as the second argument for the RIGHT function, which extracts 10 characters from the email address, starting from the right. The complete formula is evaluated and solved like this:
=RIGHT(C4,LEN(C4)-FIND("@",C4)) =RIGHT(C4,17-7) =RIGHT("email@example.com",10) ="maaker.com"