How do I get Intel?
You'll get a certain amount of Intel without even trying. Like cash, intel is dropped by enemies as loot, much like cash bundles. Just scoop up these file-folder icons to add to your store. They're usually only worth a few point each, but given the number of enemies you plow through, it adds up.
The Recon Run & Hostage rescue tasks in the city map also give you a chance to earn a handful of points each time the task is completed (though the Hostage Rescues are much easier, and much less likely to get derailed by other city events).
How do I get more Intel?
The best way to acquire intel is by assaulting LEGION outposts. Beyond any intel-as-loot, you also get a specific intel prize for commandeering the Outpost, somewhere in the 30-40 point range.
How do I spend Intel?
Intel can only be spent in Global Conflict part of the game which unlocs at level 8- you'll need to use Intel points in order to send your agents off on secret missions worldwide. The rewards of Global Conflict can be high (completing the map, for instance, is the only way to get your hands on Elite LEGION tech), so it's worth hustling for a little extra intel now and then to keep your international profile high.