Number of distinct subsequences

There is a problem with the liket code: different subsequences.

Given string S and string T, count the number of distinct subsequences of T in S. The subsequence of a string is a new string that is formed from the original string by removing some (maybe none) characters without violating the relative positions of the remaining characters. (ie "ACE" is a subsequence of "ABCDE" while "AEC" is not).

Here's an example: S = "rabbit", T = "rabbit" Return 3.

My questions:

Here I don't understand what is the point of "counting the number of distinct subsequences of T in S" I think that "r", "ra", "b" rab "," rabt ", etc. are all subsequences of T, and they are also in S. But the answer gives the answer "3." So I must have misunderstood the problem, can someone explain it to me? Just give me some typical examples and explanations in order, and don't tell me how to solve them I hope to do this as an exercise. Thanks in advance