MGeo, please, study the tutorials in the Editors Depot. ;)We're very happy to help you but there are a couple of tutorials on specifically this point, plus there is an example Briefing in the Tutorial Mission which I referred you yesterday.
There is a lot to take in when you first start mission editing, and OFPEC was created to help you do it. However, if you want to get the best out of OFPEC you have to use it properly. Go to Editors Depot - Tutorials - Getting Started and spend plenty of time there. Start with
snYpir's OFPEC Guide: making missions
macguba's guide to mission editing for beginners
and follow the advice you find there, particularly on which tutorials to read next.
The other thing you are talking about is called an Overview. Yes there is one in the Tutorial Mission for you to copy. How to make one is covered in the Briefing tutes.
The forum is the place to come when you can't find anything in the Editors Depot to solve your problem. Or, alternatively, when you have found something but don't understand it.