determine when user pressed btnSearch or ...

Question

Hi everyone
i want to determine when user pressed buttonX1 or selected a row from dataGridViewX1 then run its command.
i don't know i should look at what...
i don't know, i should use what property or...
private void btnUpdatUser_Click(object sender, EventArgs e)
        {
            if (?????????????????? )
            {

              
            }
            else
            {
                MessageBox.Show("error");
            }
         }
3:27:28 PM