Here I whipped up a skeleton Briefing for you.
Save it as Briefing.sqf into your mission folder
In your init file, add this to the very top.
For objectives make triggers and markers and name them specifically. You make markers in the editor and put their names in the briefing to hot link to them.
player createDiaryRecord ["Diary", ["Mission Title", "Detailed Description of the mission. Here is a marker <marker names="">Text here</marker>]];
obj1 = player createSimpleTask ["First Objective"];
player setCurrentTask obj1;
obj1 setSimpleTaskDescription ["Your primary objective is to reach the blank, "Objective", "Objective"];
obj1 setSimpleTaskDestination (getMarkerPos "Name of marker to go to");
obj2 = player createSimpleTask ["Second Objective"];
obj2 setSimpleTaskDescription ["Your next objective now is...", "Objective", "Objective"];
obj2 setSimpleTaskDestination (getMarkerPos "Name of marker for next objective");
obj1 setTaskState "Created";
obj2 setTaskState "Created";
getCurrent = currentTask player;
// Comments by you
For completing an objective put this in the trigger
Its quite simple, If you need anymore help just ask.
hint "Objective complete, move onto objective 2.";obj1 setTaskState "SUCCEEDED"; player setCurrentTask obj2; obj1 = true; publicVariable "obj1";
Save this as Debriefing.html in your mission folder. This will show text when your mission is complete at the end screen in the bottom left.
<meta http-equiv="Content-Type" content="text/html; charset=windows-1250">
<h2><a name="Debriefing:End1">Mission complete.</a></h2>
Congratulations, all objectives have been completed.