I don't know which website is the most popular, but in my experience (I am a native American English speaker), the website with the most effective learning of any language they offer is pimsleur.com. Their audio lessons are approximately 30 minutes each. I have used their 'one lesson each day' approach with native speakers vocalizing each word, and then the student (me) repeating their words out loud with an emphasis on pronouncing the words correctly. I've found it best to repeat each lesson as many times as needed before moving on to the next lesson. The Pimsleur "GOLD EDITION" is the version I use most successfully, with Reading Lessons in each level. This is especially good, because being able to verbally converse is only half of the journey to learn the language. For these reasons, if your first language is English, I recommend the Pimsleur method.
If the cost of this approach is an impediment, then I suggest that there are several free youtube.com channels that are almost as good (though less structured), and several of them will offer a good foundational basis to learn the French language. Some of them will enable you to learn far more that the simple basics of the French language vocabulary.
In learning any new language, however, a key success factor is practice with other speakers of the language. As with any newly learned skill, practical application is important to aid in retention.
The French people have a saying that is intended to be a humorous idiom that translates approximately to, "In order to learn the language, you must sleep with the teacher." The implication is one that I agree with; that in order to truly learn a language you must live in the culture where it is spoken. I do not disagree with that sentiment, because such "in the culture" practice is about the only way to beginning to grasp the meaning of the idioms of the culture and language.