Implementing the CommandName Property in asp.net Buttons

<asp:Button ID="StepNextButton" runat="server" CommandName="MoveNext" Text="<% $NopResources:Account.RegisterNextStepButton %>"
                                ValidationGroup="CreateUserForm" CssClass="registernextstepbutton" />

<asp:Button ID="ContinueButton" runat="server" CausesValidation="False" CommandName="Continue"
                                Text="<% $NopResources:Account.RegisterContinueButton %>" ValidationGroup="CreateUserForm"
                                CssClass="completeregistrationbutton" />

<asp:Button ID="LoginButton" runat="server" CommandName="Login" Text="<% $NopResources:Login.LoginButton %>"
                                                ValidationGroup="LoginForm" CssClass="loginbutton" />

The above button controls all have the CommandName property. I looked at the code-behind of the usercontrols (CustomerRegister.ascx & CustomerLogin.ascx) where they were used and checked for the properties "MoveNext" and "Login" to understand the behavior of the buttons but couldn't find them. Therefore I don't know what code the application is running to register new customers and login existing customers. Please can someone take a look at it and explain this to me because I intend to do a similar thing in my own application but don't know what to do. Thanks a million in advance.