The advantage to learning German online is that you can study when you want and you can study as little or as much as you want. Often German lessons online can be done for free. The drawback is that there is a limit to what these courses can teach you. Some courses are focused just on basic conversation, and others get into more advanced skills such as grammar and reading German. See Resources for some options for learning German online.
Another option for learning German is to study from books. There are a multitude of books to choose from. Some contain worksheets and quizzes, and others are more like a dictionary. The advantage of a book is that you can access it anywhere. Books are good for those who learn by seeing. Books also allow you to take your own notes on the pages and to read something over and over until you memorize it. You can also save the cost of buying a book by getting one from your local library. The disadvantage of a book is that you can't hear the pronuncation of the words.
A more traditional way to learn German is by taking a class. Local colleges, universities and community colleges offer foreign language classes that anyone can take without having to be a degree-seeking student. The advantage is you can learn from an actual person, so you can ask questions. You can also learn with other students so you can practice speaking and understanding German with real people at your same level. The disadvantage is that there is a cost associated with these classes. Costs can range from less than $100 to more than $500 depending on the class and location.
Another option is a CD that you can listen to. This is a great option if you spend a lot of time in your car, because you can learn and drive at the same time. You can purchase German instructional CDs at bookstores or online. You can also check them out at the library. The advantage is you can hear how the words are spoken. The disadvantage is if you are a visual learner, there is nothing to look at. If you want to also learn to read German, or at least recognize some words, an audio CD is probably not the best choice.
You can purchase computer software programs to help you learn German. This method is interactive and allows you to see and hear German words, phrases and sentences. The disadvantage is that you have to be at your computer to learn and that you are learning alone as opposed to with real people. German language software can be purchased online, at bookstores, including college bookstores, or at large retail stores.