@jacobtbaldwin
It's best to start by follow the tutorials that GIL has set up. They cover the important bits. Also, if you're not 100% familiar with Unity's UI system, you should go back and start there. Once you're done with the tutorials, you should start with a simple and direct goal. Do you want to build a dialogue box? Then learn everything that's involved with a dialogue box. Understand what each part does, understand how to make it display and how to customize so it shows anything you like. (for ex. the player's lvl or the name of the area you're located)
Learning Ork is just a series of small steps. Each additional bit of knowledge will expand your capability.
As far as designing a UI goes, to me, the most important thing is ease of use and readability. Lay out the data so the most important information is prominent. Do not hide anything that the player will be checking constantly. Use basic color theory so the text is always readable and make sure the design is constant throughout the entire game. (in my game for ex, I use a dark blue for all my backgrounds UI and use a white or vibrant color for the text, never a dark color)
Unless your entire UI is a custom design (like an image of a scroll representing your inventory UI) icons are pretty much a must. I wished I used more icons in my game but I didn't originally design it to be icon focused. It's something I'd like to dive more into if I'm given the opportunity to make a sequel.
Lastly, you should be aware of everything you need in your menu a head of time so you can design it all as uniform as possible. I knew most of the things I wanted when I first started designing the UI but I made it somewhat flexible so I could add things down the line. Despite that, if I wanted to add another menu option to the main menu on the home screen, I would have trouble. I would have to decrease the size of the text as well as the icons. This isn't so much a problem if your menu is a simple list but if you want a fixed design, then you need to know exactly what you need and where to place it.