[Doodil]

Toggles evil trail on me and closes the menu. I'd like it to stay open until you manually close it (by pressing 0).

After a selection was made you have to redisplay the menu:

public MenuHandler(Handle:menu, MenuAction:action, client, param2)
{
    switch (action)
    {
    case MenuAction_Select:
        {
            switch (param2)    //You can also use ServerCommand to do it directly without the client typing the command themselves.
            {
            case 0:
                {
                    FakeClientCommandEx(client, "say /eviltrail");
                    //ServerCommand("sm_robot #%d", GetClientUserId(client));    <-- Example of server command instead of fake client command.
                }
            case 1:
                {
                    FakeClientCommandEx(client, "say /evilglow");
                }
            case 2:
                {
                    FakeClientCommandEx(client, "say /robot");
                }
            }
            DisplayMenu(menu, client, MENU_TIME_FOREVER);
        }
    case MenuAction_End:
        {
            CloseHandle(menu);
        }
    }
}

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How do I make the text in the menu Toggle.

You should save somewhere which client has activated the trail and who hasn't (by defining a global array of MAXPLAYER size) and changing this value whenever he uses the menu (so right after you call the function for the trail). Once you've done that you just change your

 AddMenuItem(menu, "sm_robot", "Evil Trail");

to something like:

if (clientHasTrail[client] == true)
{
	AddMenuItem(menu, "sm_robot", "Evil Trail [ON]");
}
else
{
	AddMenuItem(menu, "sm_robot", "Evil Trail [OFF]");
}

where clientHasTrail[] is a global array of booleans, saving wether or not the trail is already active.


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How can I display commands in the menu (adding commands to the menu) based on which flags the admin has?

try something like:

if(GetUserFlagBits(client) & ADMFLAG_CHAT)
{
	AddMenuItem(menu, "sm_robot", "Evil Trail");
}

(yes only one &)
to check the AccessFlags of a client against a certain flag. If the client has the ADMFLAG_CHAT in this example, then the if-expression will resolve to a number>0, and therefore will be interpreted as if(true). If you do it this way you kinda work around the override system, so consider using CheckCommandAccess instead.

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Can anyone link me to a tutorial describing how to use sub menus?

Well you basically just draw a second menu after the first one, saving the information about what was selected in the submenu-selection itself or in a global array for the client. Just check out some of the approved plugins that already do that.