Shoutbox

What is there to not understand?

Tackle your problem step by step with logic questions, and you'll see that what you ask here is actually extremely easy...

Problem: You need to get a string from 'somewhere' so you can use it to replace a text.

How you should think:
1) That 'somewhere' is a textbox
2) A textbox is a control placed on a Plus! window
3) How do you grab text from a control placed on a Plus! window? See Plus! scripting documentation 'The PlusWnd Object'...
4) Simply take a look at the list of all the properties and functions from this object in the documentation and you'll notice the function "GetControlText", click on the link to read the details about this function.

Second problem: How to catch a button press
How you should think: Similar to the first problem and look up Events Reference > Interface Windows Events
No rocket science involved here, just some logic sense and reading...

PS: and look at other scripts...

Learn to self-study and look things up.

PS: It is not that we don't want to help, it is just that by giving you straight answers you will not learn to do anything yourself.