One great thing about starting an internet business is that you need very little up-front money.  I do however recommend that you don't waste your time trying to do it for free.  There are a lot of scams that either waste your time or end up being not free.  However, starting an internet business is much cheaper than starting any other business I can think of.

There are many ways...

1. You can market your own product or products -  With or without having a web site.  The type of product can effect how you may wish to market it.  For example, classified ad sites allow you to market your product.  The downside is that for most products, the net is full of highly competitive ads.  It is truly hard to be noticed without your own site,.  However, it doesn't have to be very fancy.  I do not recommend using free websites to promote products.  They present a very unprofessional image.  There are, however, very inexpensive ways to set up a real site.  I am in the process of setting up a page with step-by-step instructions on how to do this. Contact Me if you want me to let you know when this information is available.  The best thing to market is a unique product, but that is not absolutely essential. 
2. You can market someone else's products.  There are various ways to do this:  You can market products that you buy to sell.  This involves either you shipping the items your self or finding wholesalers willing to drop-ship products for you.  There are from what I understand, some reputable wholesalers on the net and also some sites claiming to be wholesale drop-shippers who are really middle men.  Because of this, their products cost more and are difficult to market on the very competitive internet.  Do some research first to find out who's for real.  Another option is:
3. Affiliate marketing- Companies pay you a commission for selling their products.  There are many affiliate networks on the internet, many either offering commissions from top companies,  or products that offer large commissions.  If you can learn how to market, you can make very good money doing this. If  you can create a web site that gets a lot of visitors,  you can place ads on your site.  Another way to promote these products is by buying clicks on pay-per-click search engines.  Many of these search engines are a waste of money.  The best (generally most expensive) ones generate real sales.  But you have to watch what you pay, so that it doesn't exceed what you make.  Most affiliates furnish information on what to put in the ads, but I think if you are creative, you can stand out from the pack and make more money.  It really is very exciting to go to an affiliate site and see the sales you made!  Some sites even give you some information on what country the sale was made to.  See below for the section on Clickbank.

A couple of good affiliate programs:
          Corey Rudl's Internet Marketing Center - This site has several affiliate products you can market.  It also has a lot of information on how to market.  Signup is free.  They want you to sell things for them.  You can sign up if you want, before you have a web site or large mailing list.  There's some excellent beginners marketing advice on this site.

          Google Cash - An Ebook ($49.95 and worth it)  This describes how to post ads on Google (The largest search engine on the internet) to make money with affiliate programs.  I know this works, I do it all the time.  The book comes with a 90 day money-back guarantee.  If you follow the instructions in the book, you will make money.  It's a great resource because there are techniques to optimize your profits and sell more, that really work.  (You don't need a web site to do this- you can refer clicks directly to the affiliate program).

For some extra income that requires no marketing skills at all, you could try this service:
Survey Scout :  This site provides information on over four hundred paid survey sites.  They have lots of ways to make money by filling out surveys and joining focus groups.  There are scams on the internet about paid surveys.  These people only recommend the real paying survey sites that they have evaluated for you.  The service costs a on-time $34.95 fee.  Again, I think it's worth it.  Also, they have a 90 day money-back guarantee.

One of the Top Affiliate Programs On the net is Clickbank .  They offer over 10,000 Digital Products that you can market in a variety of ways.  They handle receiving credit card payments.  You just pick as many products as you want to market.  They even rank them according to popularity.  You get paid quicker than any other program I know of.  Also, if you have, or are planning to have a product that can be downloaded such as an ebook or software - or a site that charges for membership, you sign up with them and you have access to thousands of people marketing your product.  This is a definitely great opportunity.  And of course, it's free to sign up.  Click Here To Get Started!