The invention of the internet has made everything easier right? You can now shop online, send letters, find information at the drop of a hat, even find your house in satellite pictures on Google Earth. However, you would of course think that as learning a language involves speaking, this is something you would not be able to do online. You would be wrong. If you type learn Spanish online into Google you get approximately 72 million results. Now as with anything else, I am sure most of these are useless but you see my point.
There are now many websites that allow you free access to conversation exercises and vocabulary drills among other things. My personal favorite is LearnSpanish.com. I am sure it is structured much like its competitors however when I find something I like I tend to stick with it. This site allows you access to an amazing amount of drills and exercises for free. It of course also has another more extensive version that you have to pay for as I am sure most of the websites do.
So you can very simply sit in front of your computer and commence your lessons. My one recommendation though, is that if you plan to learn Spanish online, do not do what I did and go to an internet caf to do so. If you do not have a computer try to find a friend that will let you borrow a laptop or come to their house to study. Trust me when I say it is very difficult to do pronunciation drills with modals test 20 people who all speak the language perfectly sitting around and looking at you like you have lost your mind.
Of course it is probably close to impossible to actually learn Spanish solely online as it is quite necessary to hear the pronunciation and practice with actual human beings in order to be able to carry on a conversation. However if you are looking for some base knowledge to work with the internet provides a wealth of possibilities.