I use short fins about half of the time, and am slowing phasing them out. Fins help you build leg strength, but there are pros and cons to using them, especially for a beginner swimmer:

Pros:
• Helps build leg strength (greater resistance)
• Fins allows your body to process more oxygen, for a longer amount of time, building endurance
• They allow you to focus on your upper body technique/stroke, as fins act as a slight flotation device.

Cons:
• You cannot compete in fins
• You can become dependent on them