some hints:

they often say: prove by induction that this statement is true for all ..

that becomes your base case..

more often than not, they say that the statement is true for all natural numbers, thus n=1 is your base.. (but others say it should be n=0.. however, by convention 0 is not a natural number)

EDIT: it just depends on what principle you use.. try reading Principle of Mathematical Induction