Hi Austin! Welcome to the AC Forums!
Root is opening your phone's system files for modification. It's like leaving the vault door of a bank wide open. If you do this, you can install apps and modifications that make deeper changes to the phone and cad add extra functionality. However, like the bank analogy, it's not without risk since you might end up modifying critical files or leaving your phone more open to hacks/attacks.
A phone being 'unlocked' only means that it's no longer tied up to a specific carrier and will let you work with any SIM Card (or IMEI registration if you're using a CDMA phone/network) of any supported network.
Hope that clarifies things a bit, but if it doesn't, don't be afraid to ask!
We're all here to help