If you need to learn French fast, songs are a useful tool. Whether they're part of a larger language program or not, they can be very helpful in learning common phrases. They also help you to learn to put words together in the right order. English and French differ significantly in how this is done. Through song, you have a way to learn these important concepts and a way to provide an easy form of recall for everything you do pick up. When speed is an issue, this can also take a lot of stress out of the affair.
If you want to pick up French in a hurry, memorization is generally not the way to go. Long lists of words and conjugation exercises with verbs do have their place, but they're not a good way to learn fast. Most people can simply listen and learn French and enjoy much faster results. This is because listening challenges you to understand what's being said without giving you time to translate every single word in your mind. This is actually a very important step toward fluency. Fluent speakers do not translate words in their mind; they simply understand their second language instinctively.
Anyone can develop this type of fluency if they use the right techniques. The vast majority of the occasions you use your French skills will likely involve speaking, not writing. Speaking is also a bit more difficult, as you have to learn new ways of using your mouth to voice words and your ears have to become sensitive to new sounds. You learn French fast when you simply dive in wholeheartedly and rely on minimal translation to help you understand. Songs, because they are expressive and sometimes poetic, can convey a lot of meaning in few words, making them useful for understanding new languages.
If you want to learn in the French classroom fashion, with rote exercises, you'll probably find yourself putting in a lot of effort before you see any reward. Listening to songs and learning to sing them is actually entertaining, which makes it easier to learn. When you're enjoying something, it's much easier to learn from it. Remember that language learning never has to be a tedious affair. With the right materials, it can be a lot of fun and you can become fluent much more quickly than you likely believe.