Transpose or Copy Text from text to another Text box and Undo when necessary

[TechGeek]

G'day!

This might be a bit easy for you guys but I need your help to get the right code for this.

I have 2 text boxes and 2 CommandButtons
TextBox1 and Textbox2 and Add Button and Back Button
I would like to transfer or dump all of the text I put on Textbox1 to Textbox2 and be able to add more another set of text after I click on Add button.

Example:

I typed "Please help me" and pressed on Add button.
TextBox2 should have "Please help me" on it.
Then I typed "I need help" and pressed on Add button again.
TextBox2 should have "Please help me" and "I need help" on it.
if I am going to click on back button, I should only see "Please help me" on the text box.

Olease help me with the right code for add and back buttons to function as stated above.