[Ranama]

here you go:

https://sampwiki.blast.hk/wiki/ShowPlayerDialog

ShowPlayerDialog(playerid, INFO_DIALOG, DIALOG_STYLE_MSGBOX, "My title of my cool messagebox", "Server rules:\n don't go to my place\njust shoot on admins\nDon't have fun\nEtc.", "Okay", "");

Hope you understands how to do it.