When I started teaching myself photography, I quickly learned that controlling the Aperture was what was going to give me that "emotional" element to my pictures that I wanted, either that blurry dreamy background or sharp and crisp.
A big aperture -- or a big opening (which confusingly is a low f-stop number, like f.2) makes for a shallow depth of field (dof) or blurry background --great for portraits.
And a small aperture (high f-stop number, f.22) makes for a clear and crisp background, better for those landscape shots usually.
If you are starting out trying to learn the basics of photography, I would start with aperture and get really comfortable with that concept and how to control that on your camera. The other thing I would do is read your camera manual about 1000 times so you will know how to set that without having to stop and think about where the button is and which way to turn the dial.
Here's a link to a great tutorial which explains aperture: DPS Explains Aperture
And this is a cool simulator which visually explains aperture: Aperture Simulator