The standard camera app that came with your phone is fine, and it won’t let you down. But if you want to get great shots with your phone, you’re going to want to upgrade to a better one. Third-party apps generally offer more settings, like allowing you to set the focus and the exposure of your photo separately, take burst shots, use different flash options, and more.
There are lots of different third-party camera apps out there, but some of the biggest names are Camera+, Manual, ProCamera, Camera ZOOM FX, and Camera 360. You’ll probably need to pay a couple bucks to get one of these apps, but the improvement in your photos will be absolutely worth it (I’ve been using ProCamera for a while now on my iPhone 6, and I highly recommend it).