The Apex Boost is a single-use item that temporarily multiplies AP earned while the Boost is active. A 2X version of the Apex Boost is currently available. 
 
Once activated, an Apex lasts for 30 minutes. The map screen will show a timer indicating the time remaining on an active Boost. 
 
To use Apex Boost:
  1. Open the inventory carousel
  2. Swipe right to the Boosts category
  3. Tap Apex
  4. Tap Use then tap Confirm

You can activate multiple Apex at once, extending the AP multiplier to a maximum of 2 hours.