If you can't find the controls to change for shutter speed, ISO, or white balance, you're probably in "Automatic" mode. You can tell by the triangle on the top of the screen.
Tap on the triangle and a panel will slide out, allowing you to enter manual mode.
What about Aperture?
All iPhones have fixed apertures. However, if Apple ever releases an iPhone with adjustable apertures, we will support it in Halide.