You can learn to speak Arabic by taking courses, using specialized software such as Rosetta Stone, or teaching yourself by studying books and using various mobile applications. If you are seeking to become fluent, you likely need to build upon this book knowledge by participating in a language immersion or an intensive language course. Typically, these types of experiences are completed as part of advanced degree programs, but some programs are available to all.
Rosetta Stone is widely acknowledged as the premier language learning software. Rosetta Stone's courses can provide a solid foundation of Arabic for beginners and can hone the skills of advanced Arabic speakers as well. Similarly, there are a number of free online tools and mobile applications that can serve the same purpose, such as Salaam Arabic and Learn Arabic by AccelaStudy. Some major universities and some smaller colleges and community colleges also offer classes in Arabic.
While all of these learning methods are good places to start, if you want to become fluent, you need to engage in conversation frequently. One great way to do this is to take an intensive language program, such as the ones offered at Middlebury College in Vermont or the Monterey Institute in California.
If, however, you already have moderate proficiency, hone your skills and become fluent via language immersion in an Arabic-speaking country. These programs can typically be found through universities, but there are also private companies that have study abroad programs.