Question: I've seen a lot of different topics and suggestions on aligning and inputting buttons/text, but the ways I've seen seem kind of risky.

What is the optimal way, for example, to add two buttons, stack them together, and have them be 10% from the bottom of the screen, and centered horizontally on all devices?

Answer: 
Your best bet is to use [Auto Layout](https://developer.apple.com/library/mac/documentation/UserExperience/Conceptual/AutolayoutPG/index.html). It takes a bit of learning but once you get used to it you can add constraints pretty quickly and easily in Interface Builder. I can't recommend any particular guide but there are a lot of good ones to be found with a quick Internet search.

Here is an example of constraints that seem to be what you are looking for:

[![Auto Layout Constraints](https://i.stack.imgur.com/JVDZX.png)](https://i.stack.imgur.com/JVDZX.png)
[![iPhone 4-inch Portrait](https://i.stack.imgur.com/K9SaD.png)](https://i.stack.imgur.com/K9SaD.png)
[![iPhone 4-inch Landscape](https://i.stack.imgur.com/YmzIQ.png)](https://i.stack.imgur.com/YmzIQ.png)
For iOS 9, an even simpler Auto Layout approach would be to use [UIStackView](https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIStackView_Class_Reference/).

As you can see, no constraints are needed for the buttons embedded in the stack view, as the stack view lays out the buttons for you. All you have to constrain is the location of the stack view itself.

Here's an example of two vertically stacked buttons, 10% from the bottom of the screen, and centered horizontally for all devices.

[![enter image description here](https://i.stack.imgur.com/izHwx.png)](https://i.stack.imgur.com/izHwx.png)