He didn't specify online but still, I have to say the only way that's worked for me is to LIVE in the country using and hearing the language constantly. For Spanish, make sure whatever you use to learn it is the same dialect you'll need too. Puerto Rican Spanish is very different from the Spanish spoken in Mexico and from the Spanish in Spain. Reading and writing it is way easier of course.
Whatever method you choose, it may help to buy a couple of videos in Spanish so you can hear it used more naturally than in a language program. Don't be discouraged if you miss every single word at first, it'll come eventually!