What is the third term of the sequence defined by the recursive rule?
f(1) = 2 f(n)= 2f(n-1)+1

The way you worded the question kind of confuses me but i'll try to answer.

Think of recursion like climbing a ladder; in this type of sequence you start out somewhere, usually n. So in f(n-1)+1, you take n (where you started) and "step down" once, and then step up once (which brings you back where you were). Remember PEMDAS when doing these.