VBA Loops + Arrays

Hey guys, I am a student and am taking a class in VBA modeling. I've had one assignment prior to this one where I had to use a Do loop, but other than that I am not skilled in VBA whatsoever. I was hoping I could post the description of the project and get someone to lead me in the right direction. This assignment requires the use of Arrays, and I do not understand them at all as well as other parts of this project. Thanks in advance for any help.

The finished product should have two boxes, one for the encrypted data and one for the un encrypted, and also two buttons, one to encrypt and the other to un-encrypt.
Suppose we want to encrypt data for security reasons. Assuming the “data” entered is always a 4 digit integer, write a program to encrypt the data as follows: replace each digit by (the sum of that digit plus 7) modulus 10, then swap the first digit with the third and swap the second digit with the fourth. Print the encrypted integer in the box (Hint: to build a sting of integers, use the concatenate symbol &). For this assignment, you must use an array to store the four values, and put it within a loop for extracting the values using the MID function. Next, write a routine to decrypt a number back to its original value.