Crack the code? i don’t understand

Whatever the mind can conceive and believe the mind can achieve.

Step-by-step explanation:

Start with the letters SFV you know the middle letter is N - aside from "the"  which is the most popular three letter word "and" is the second most used three letter word.   That means the letter S is an A and the letter V is N.   So EAFV  would read M ND.  You know its not an E or A, that leaves I, O & U.    After plugging in those letters you have part of a sentence THE MIND _AN.  If you plug in the remaining letters you will see that the letter C makes the most since.  THE MIND CAN.  With that information you will be able to figure out the rest.