From what I have seen so far, these excercises are just math and programming algorithms but applied to the field of bioinformatics, the first problem (take a DNA string of length S and count the number of time each letter shows up, output total count) is a problem that most teachers put on the homework in 2nd semester programming courses.
So I guess my advice to you would be to just ask your question, and see if anyone can help. I know for a fact that there are quite a few people on here more than capable of helping you understand the problems that you don't quite get.
