Very important to learn: convertion from code to boxs

Question

Hi!

Please how can I send my SMS throught Textboxs and combobox? I am asking this simple question because I must insert in that line of code in red the cellnumber(s). But I don't want that way. I need a professional way.

user = txtUser, password = txtPassword; api_id = txtApiId; cellphone= cbxCellnumber; message = txtMsg

string baseurl = "http://api.clickatell.com/http/sendmsg?user=[x]&password=[xx]&api_id=[xxx]&to=[xxxx]&text=Message" + to + "'&text='" + msg + "'";

 private void button1_Click(object sender, EventArgs e)
        {
            try
                 {
                WebClient client = new WebClient();
                string to, msg;
                to = textBoxTo.Text;
                msg = textBoxMsg.Text;
               
                string baseurl = "http://api.clickatell.com/http/sendmsg?user=[x]&password=[xx]&api_id=[xxx]&to=[xxxx]&text=Message" + to + "'&text='" + msg + "'"; // This line here
                client.OpenRead(baseurl);
                MessageBox.Show("Message sent");
         }
            catch (Exception ex)
         {
                MessageBox.Show(ex.Message);
        
}  


 }
 }
}