Addition and Subtraction

Can someone help me how to code addition and subtraction?
for example, user writes a number on the first textbox, and another number on the second textbox, I want both numbers to be added and appear into a third box (or label)

Hello,

you can use textBoxes for input data, mathematical blocks for the operations and a label to display the result. Try it, and let us know how it goes.

thank you!
do i use 'when textbox .textchanged'?

you can use a button "Addition" and other button "Subtraction" and when the button is clicked, then take the data from textBoxes to execute the mathematical operation (addition/subtraction, regarding on the button clicked) and display the result.

Search the Gallery for 'calculator'

It will probably not work with textbox.textchanged. I would also suggest the method that Ramon suggested. It can also help differentiate between the two operations.