The formula "a + (n-1)d" is used to find the nth term of an arithmetic sequence. In this formula, "a" represents the first term of the sequence, "d" is the common difference between consecutive terms, and "n" is the term number you want to find. For example, if the first term a is 3 and the common difference d is 2, you can find the 5th term by substituting these values into the formula. This gives you 3 + (5-1) * 2, which equals 3 + 8, resulting in the 5th term being 11.