The game starts you off with a kinetic weapon equipped. Press the △ button to switch to an energy weapon.
Each press of the △ button henceforth will switch between kinetic and energy.
Switching to a power weapon, however, requires that you hold the △ button. From there, tap the △ button again to return to kinetic.
The topmost weapon icon in the bottom left of the screen shows which weapon is currently equipped.
The image on the right indicates a power weapon is equipped.
Your firearm will be automatically held near the hip, as long as you're not pressing any buttons. Hitting R2 button in this state discharges your weapon without using its sights. Some weapons actually have higher accuracy when fired from the hip.
Pressing the L2 button will aim down your sight, zooming in and making it easier to hit foes. This mode is good when attempting to score precision hits.
There are some downsides, however. ADS slows movement, rendering enemies already in close proximity harder to hit. Your radar also disappears. Thus, staying in this mode for an extended period puts you in serious danger.
Here's an example of a tried-and-true approach to combat. Use a kinetic weapon as your mainstay, switching to an energy weapon when a shielded baddie pops up. After destroying the shield, switch back to kinetic to deal precision damage.
And should you find yourself surrounded or up against challenging enemies, break out a power weapon to inflict some widespread hurt.
Knowing which weapons to use, and when, is crucial to overcoming the many trials ahead!
*Screenshots shown are from the Japanese version. The game is playable in English.