Surveys can be performed in many different ways. I'm sure that most people have been approached in the street, at some time, by researchers armed with a clipboard.
Others ways include phone and mail-in surveys, but by far the most common now-a-days are the online surveys.
Unfortunately it is not as easy as just finding a few companies that offer surveys, signing up and then participating in surveys all day long. It's all about demographics.
The reality is that you may only get a few surveys to complete each month. It all depends on what market research is going on and whether you fit into the required demographics. For example if a company is researching baby clothes and you do not have children then you won't be asked to participate.
Even if you do qualify for a particular survey then it may be that all of the positions in that survey have been filled.
A typical survey will take you somewhere from a couple of minutes to 20 minutes to complete. You'll earn more money for the more detailed surveys.
You could earn up to $2 per survey but most will get you only a few cents. You are never going to become rich by taking online surveys, but you may be able to make a little extra pocket money.
Some companies may not offer a cash incentive but instead will give you the chance to win a prize, enter a sweepstake or gain gift points redemable against certain goods such as electronics. Whilst this may sound a good idea, I presume that you are at this site to find ways to make money online, so it is better to avoid these options.
In rare cases you may be sent physical products so that you can give an honest opinion of them, but this is normally only reserved for respected long serving survey participants.