this problem is not hard. i don't rember the detail about C right now, but i can give you some ideas!
1. write a function: menu -use printf
2. write a function to distribute the jobs.
   in the function, you can use switch
   switch(option)
   { 
        case 1: newCustomer();
              break;
        case 2: search()
              break;
        case 3: displayAllCustomers()
              break;
   }
3. write each sub-functions
  int newCustomers()
  {
     //use scanf to get the information from customers
    // use if else to ask wether the user wants to save
       if yes,  use fprintf or fputs to save into the file
       else  return;
  }
4.
   int search()
  {
    // use fscanf or fgets to get data from source file and store them by using pointers
    // you can search by name by using some algrithms. this depends on how you store the data
    return 1 if you get it. otherwise, return 0;
   }
5. void displayAllCustomers()
  {
      // this one is actually the first part of search
         you should get data from file. then print them out( you can use fscanf and fprintf here)
  }
i hope this can help you!! GOOD LUCK FOR YOUR TEST