If you continue to use Shareware after trying it out, you are expected to register your use with the author and pay a registration fee. What you get in return depends on the author, but may include a printed manual, free updates, telephone support, etc. Only by paying for the Shareware you use do you enable the Shareware author to continue to support his software and create new programs. Considering that the Shareware registration fees are almost always far less than the purchase price of comparable commercial software it's obvious that Shareware is a good deal for everyone.
Shareware is a distribution method, not a type of software. You should find software that suits your needs and pocketbook, whether it's commercial or Shareware. The Shareware system makes fitting your needs easier, because you can try before you buy. And because the overhead is low, prices are low also. Shareware has the ultimate money-back guarantee -- if you don't use the product, you don't pay for it.
There are real advantages to you in the Shareware system. You get to try out software to make sure it is compatible with your hardware and that it fits your needs before you "buy" it with your registration. The author saves the expense of advertising, packaging and distribution and passes the savings on to you. Plus, most Shareware authors are much more accessible than commercial software sources so that your questions and suggestions are much more likely to be responded to.
Depending on the specific product and version, a shareware release may be distributed in a fully functional form or in a demonstration form sometimes known as "crippleware." This latter type of shareware is distributed with certain features which remain disabled or reduced in function until the user pays the shareware licensing fee and receives an authorization code from the software developer.