There are a total of 45 Intel Locations in Call of Duty Advanced Warfare. Finding all of these collectibles will earn you the "Ferrum Absconsum" trophy or achievement. In mission select you can see how many you have found in each mission.
The intel collectibles look like thin laptops with a blue display.
None of them are missable! You can search for missing items via mission select at any time during the story or after beating the story.
As soon as you pick up an intel it will be saved immediately and automatically. You don't have to reach the next checkpoint and can quit out to the main menu right away. There are exactly 3 intel collectibles per mission.