How 2 make a button action so that it makes a word visible on an inputtxt

Very familiar with audio editting and stuff, also design (no flash e.d.) So beginning to learn bit by bit.
I now actually understand that the hardes part of all nice things are coming this year for me. the variables, let animated things work.

A question I have is:

how 2 make a button action so that it makes a word visible on an inputtxt. (Some sort of add 2 cart, a button action adds a text into an inputtextbox. When all products are chosen the send button at the bottom of the form will send it 2 email. (trough php)

All of that is fixed accept that code.

Is it possible when the buttons are in load level 2 and the form is in 1.? (So that those buttons can preform the action 2 goto that form and fill in my desired button related text)

Greets,

a music hippy.