Hey Diego!
It seems that you want your app to perform different operations as a response to UI events that occur. Luckily, performing an action as a response to a change is the exact role of a call back function that can be attached to various UI components.
In MATLAB App Designer, you will notice that each component you drag onto the UIFigure will have properties shown on the bottom right of your screen. If you click on the 'CallBacks' tab, you will be able to enter a name for a custom callback function for each component. In your case, you would need to do this for each EditText/Button object that you would like to monitor for changes.
Once complete, you should be taken to the code-view of the application where you can write the implementation of the function you have just named. This is where you would save variables, disable buttons, or modify text as you see fit.
To see a full list of the operations you can perform on various components, check out the documentation: http://www.mathworks.com/help/matlab/components-in-app-designer.html
Hope that helps!
