There are several ways to get them:

1. In your base, you can build Metal Extractors, Oil Refineries, Chemical Plants and Thorium Plants. Once you've built them, you can collect resources from them. Upgrade these buildings to increase their output.

2. On the World Map, you can look for randomly spawned resources. Select one of them and tap "Gather" to send a certain amount of your army to occupy the resource and gather from it. The amount of gathered resource depends on the army's Load Capacity.

3. On the World Map, you can look for Elite Deposits, which have more resources. To be able to "Gather" from these, you have to be in a Faction and the resources must be in your Faction's territory. Keep in mind that when mining from a Faction Elite Deposit, your gathering speed is increased by an additional 30%.

4. Attack Renegade camps on the World Map.

5. Complete missions.

6. Ask a Faction member to send you resources (see Assist).

7. Complete Black Ops.

8. Collect the Daily Supplies.

9. Complete Daily Missions.

10. Faction territory reward based on your Faction's size (in tiles).

11. Limited-time events.