From the Press the Attack announcement page it talks about the card "Endor Command Post." It generates a resource and its text reads: "Action: Focus an Officer unit to remove 1 focus token from this enhancement."

To quote the article...

"...perhaps one of the best ways to use the Endor Command Post is in conjunction with Grand Moff Tarkin(Imperial Entanglements, 872). Blanking enemy cards repeatably with the Endor Command Post and Grand Moff Tarkin can be a powerful asset in your battle to defend the shield generator."

I can't follow how the two cards are supposed to work together. If I focus Tarkin to free up the Command Post, how does that also use Tarkin's ability?

I think you'd focus Tarkin to free up the Command Post so you could then spend its resource to pay for Tarkin's effect.

LightningFox has the right of it. Tarkin doesn't have to be ready to use his Reaction, so the idea is that you focus Tarkin (or another Officer) to pay the cost of Endor Command Post's Action during the last action window of a phase, and then you have an Imperial Navy resource to pay the cost of Tarkin's Reaction at the beginning of the next phase.

The reason the combo was pointed out is that it allows you to spend all of your resources on your own turn and still have the ability to threaten Tarkin.

Probably best focusing another officer. Focusing Tarkin to free up the command post doesn't net you a resource (since Tarkin could focus to produce the resource anyways).