How to publish my game as shareware

1) Put the limited free version out on your website, filesharing networks, etc for free, include a way to buy the full version (These days a simple button that links to your webshop is enough)
2) Sell the full version somewhere (There are plenty of e-commerce solutions you can choose from that help you do this)
3) Profit

As for the legal side of things you normally only need to register a business for tax purposes(Check with your local authorities), as for licensing thats really up to you, copyright is automatic and sets the basic rules for you but you will have to atleast have a license that grants users the right to make and distribute copies of the sharable version(as copyright prohibits this normally).

a lawyer should be able to write a suitable license for you fairly cheaply.