The first thing would be the obvious, create your map.
Now we need to add some hosties.
Choose your entity tool and choose hostage_entity as your entity to use. Place your hostage entity wherever you like.
NOTE: There will be no visible model. All you will see is a red block.
While the entity is still highlighted press alt+enter to bring up your entity editor window. Here you can choose the angle your hostage will face and what model it will use as your hostage. Hostage models are A,B,C, or D I dont know off hand which one is which.
Now that you have your hostages placed all thats left is your extraction zone.
To do this we will first lay our hostage rescue decal. Click your add decal button from the toolbar. Next open the texture browser from the right pallette and do a search for decal. about 2/3 of the way down you will see the texture "decals/hrpoint", select that texture. Now in the 3d view simply click on the ground and that texture will be applied to that surface.
Now we will add the hostage extraction trigger.
Ok make a brush to fit the size you wish using the trigger texture. once this brush is created click tools from the top toolbar and choose tie to entity. from the dropdown list choose the entity func_hostage_rescue