Composition Tools
Exposure and color get a lot of attention in photography, but composition is the decision you make before any of that. It's why we put these tools front and center in Mark III's toolbar, within thumb's reach.
Now we'll cover everything in that toolbar: the composition guides, the aspect ratio picker, and the level tool.
Composition Guides
Tap the grid icon to overlay a composition guide on the viewfinder. Mark III ships with four:
There's no wrong choice, so play around. Many photographers settle on one guide and stick with it for months, then switch when they want to push themselves. Try each one for a day and see what feels natural.
Aspect Ratios
Tap the aspect ratio button to choose the shape of your frame. We've drawn these from film photography. 
The Level Tool
The level indicator appears in the viewfinder as a subtly lined box or cross that turns solid yellow when your phone is perfectly vertical and an overlayed dot when the phone is perfectly horizontal.
It's most useful for architecture, landscapes, and macro shots, where a tilted horizon is immediately obvious. For street photography or portraits, a slight tilt is often intentional, so feel free to ignore it. You can turn this tool on or off by tapping on the Grid icon and tapping on "Level".
Lesson 3: We'll get into RAW - what it actually means, why it matters, and why you might choose to turn it off.