Get some money from creating and manage a web page, how does it works?

Depends all on what you want to do. I work freelance for a few small and some bigger companies and just do some maintainance on their websites occasionally, and just send them an invoice after every update, or for some of them every month. I do this next to my fulltime daytime job as a workshop technician (with no computers involved at all, whoohoo!)

Another way is to create a website that pulls in a lot of visitors because of whatever features / content you have, and then monetize that in some way. Popular ways are having paid accounts for your users that have more features then the free accounts, or having Google Adsense ads or other banner ads that pull in some money.

If you have a popular blog you can also get paid for writing reviews about products or other sites. Reviewme.com is a site that allows you to review services and get paid for it.

Or, if you have a very good site you can hope some company buys the site from you for a bunch of money, like Google bought Youtube and Yahoo! bought Flickr, and so on.

Rule of thumb is though, you need to invest and have a good plan in order for it to work.

Apart from the answer above

Try guru.com, elance.com and rentacoder.com

There you can put together proposals for people looking for web designers.

Make sure that you have your own web site with some of your designs on it. That way you can demonstrate your capabilities.