How can I create an apache web site

What distro are you using? Do you want it available to the outside world?

Anyway, the general steps are:
1) install apache
2) build a web page
3) put that page in the document root
4) Tada!

My distro is ubuntu.
I already install apache.
But wat a must do next.

I put the address localhost in the browser and than the apache page appears

The next step would be to post the specific problems you have with the next step.

- You're probably looking for Apache's document root? - That's /var/www on Ubuntu.
Are you serious??

No I mean: what I must to do next.

Put some HTML or text file into Apache's document root.

Locate Apache's Home folder and add sample contents
You need to be root to put files to that place. I.e., in a terminal, type,
The file manager Nautilus will open that folder, and you can create some file there by right-clicking, "Create document >> Empty File".
A file will be created.

Double-click it and enter some random text. Save, and close the editor.

Rename the file to "test.html" by right-clicking it in Nautilus.

Enable web users to view it
Right-click the file, select "Properties", and a dialog will pop up. There, choose the tab "Permissions", and give "Others" "Read" permissions.

Test the results
Next, point your browser to http://localhost/test.html.

I do that and works. But I still have the page test.html in my computer not in apache server...

Please, be more specific!

We really cannot know what you mean. - Your messages are too short and not specific enough.

- Thanks for your understanding.
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What exactly did you do?
What works, exactly?
That's not understandable to anyone. Make it absolutely reproducable to the readers, else, forget it.

- Is this the first time you're requesting support?

What I mean it's that the test.html page appears in the browser. But this page is in the computer not in apache serve. I want create a web site in apache, in apache server. A page that can be see in any computer. A page online. I don't know if that is possible...
Sorry my english!

Thanks, I understand. - Usually, people host their web pages at remote servers, by contracting with an internet service provider. Keyword: "web hosting".

You apparently want the files on your computer being accessed remotely, by other people.

What's the output of
and how do you connect to the internet - using a DSL provider? - sharing a DSL line with others? - being in a corporate network?

I have a connection DSL.

Good to know...

have a look for "Dynamic DNS" so you can point a URl to your system
Huh? if you can see it in a web browser, then it is on the apache server, as your system IS the apache server.