Since I have been in photography understanding lenses have always been a constant struggle for me. Understanding the applications for each focal length has always been difficult, but it is definitely important that you understand the lenses that you use.
What is Focal Length? The focal length of a lens measures the distance between the lens and the image sensor, measured in millimeters. Lenses can be classified into subgroups like prime, macro, wide angle, normal, telephoto, and zoom lenses.
The only advice I would give would be. Every photographer shoots different. One lens that is great for one photographer could be detrimental to another. I would try or rent the lens that you desire and real use it at a shoot. This will help determine if it suits your shooting style and if its the right lens for you.