If i am not wrong then you want to add your textbox value to some ohter textboxes. If It is so then here you go:-
On button_Click write following code:
protected void button_Click(object sender, EventArgs e)
{
string firstvalue = textBox1.Text;
textBox2.Text = firstvalue;
textBox3.Text = firstvalue;
label1.Text = firstvalue;
}
I hope it will help you.
Good luck.