Suppose you want to prove something for integers >= 2. E.g., suppose you want to prove for all n >= 2, n is positive. The statement you're trying to prove for a given n is actually
P(n) := n >= 2 -> n is positive
Let's prove it by induction.
P(0) is 0 >= 2 -> 0 is positive. P(0) is vacuously true, because 0 < 2.
Suppose P(n). We want to show P(n + 1). Our goal is
n + 1 >= 2 -> n + 1 is positive. Let's break this into the cases n >= 2 and n < 2.
For n >= 2, we assume P(n) and have the LHS of the implies. This gives us n is positive. Say by definition or by a lemma that n positive -> n + 1 is positive, and we handle this branch.
For n < 2, the inductive hypothesis tells us nothing. Assume the LHS of our goal, i.e. n + 1 >= 2. We want to prove n + 1 is positive. Well 2 is positive and therefore n + 1 is positive by transitivity.
This is what I mean by the base case not being special. E.g., in Coq, induction over the natural numbers always starts at 0. When you think about doing induction starting at another number, you're transforming your goal to include something of the form n >= m -> P(n).