<asp:Button ID="Button1" runat="server" Text="Button" />

When button is clicked then click event is fired.

We can provide an event handler for the Click event to programmatically control the actions performed when the button is clicked.

<asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Button" />
protected void Button1_Click(object sender, EventArgs e)
{
 Label1.Text = "Hello";
}

Here, when we click the Button then it will display message “Hello” in Label1

We can change button appearance

<asp:Button ID="Button1" runat="server" Font-Bold="True" Font-Names="Arial" 
Font-Size="Larger" ForeColor="#FF66FF" Text="Button" />

Font-Bold property of Button Control is use to make font bold. If we set its Font-Bold property to True it will make text of Button Bold and if we set it False then it will not.