Let's see what we can get by dividing 625 by 5, as it ends with a 5:
625/5 = 125
So we have 5 as one of our factors. Let's divide again by 5:
125/5 = 25
Our current prime factors now are 5 and 5, but we aren't finished. Divide again by 5:
25/5 = 5
Now we know that the prime factorization of 625 is 5 * 5 * 5 * 5, which can also be shown as 5⁴.