UV unwrapping is like the reverse of wrapping a gift. When you wrap a gift you have to consider the best locations for the edges of the paper to connect. UV unwrapping is similar to opposite process.
You're going to have to practice to understand UV unwrapping and computer graphics in general. Use the stretching visualization to test seam locations. If your unwrap shows your faces as blue, then you've found a good seam location. If your faces turn out red, it's a bad seam location.
