Well, I'm a pretty new to most of this as well, so I won't criticize your soldering.
Until I built my first USB dongle last week, I hadn't soldered any kits together in over 20 years. My last kit was a simple adjustable power supply in high school. As far as I can recall, I had never used flux cleaner until last week. If you want to see bad, you should see the welds on the wireframe snowman I assembled a couple weeks ago. On second thought, I may have to blur those parts of the pictures out if I upload them somewhere for people to look at.
From your picture it looks to me like a lot of flux from using a bit too much solder, but I'll let the soldering experts correct me if I'm wrong.
I picked up some MG Chemicals spray-on flux cleaner to clean my boards up, but there are other options. I think if you search for flux cleaner on here or on your favorite search engine and you'll find a bit of input and how-to's.