Now that you have read all of this information into a data structure you will need to have the ability to make use of it. Your next task for this lab will be to define an interface to accomplish this. You should offer the user a number of choices and provide answers to their queries. One of the chief difficulties in answering a user query will be to find the relevant information. E.g. if the user wants to know how many classes student 1500 asked for, first you need to locate student 1500's record.
Binary search is one of the simplest and most powerful algorithms in computer science.
The idea is that we compare what we are looking for to the item in the middle of the sorted data structure. If our item is less than that item we know that it must be in the second half of the data structure. If it is greater than that item we know it is in the first half. Thus we have eliminated half of the data structure with one comparison. You can find a discussion of this algorithm and some basic code for it on pages 127-128 of your book.