Capturing a Portal allows you and members of your Faction to create Control Fields by linking that Portal to other Portals controlled by your Faction.
To capture a Portal, you’ll need to deploy Resonators. Resonators are XM objects that power-up a Portal and align it to a Faction. Resonators can be deployed in the 8 slots around a Portal. When one Faction deploys 8 Resonators, anyone from that Faction can establish Links to and from that Portal.
Resonators range from level 1–8. High-level Resonators are harder to destroy, but you can only deploy a limited number of them to a single Portal. The highest level of Resonator you can deploy scales with your Agent Level.
Gaining control of a Portal also lets you deploy Mods, items that help defend Portals against attackers from the opposing Faction and provide other bonuses.
You can tell which Faction has captured a Portal by its color:
Blue Portals are controlled by the Resistance.
Green Portals are controlled by the Enlightened.
Grey Portals are neutral (i.e. controlled by neither Faction).
To capture a Portal controlled by the opposing Faction, you’ll first need to attack the Portal and destroy all deployed Resonators. You can start deploying Resonators as soon as the Portal turns neutral. You can also use an ADA Refactor (if you're Resistance) or JARVIS Virus (if you're Enlightened) to instantly flip the alignment of a Portal.