I wana add a new Clean Page, like http://hompage/cleanpage. If i add a Page through the Sidebuilder, the link to this Page will display under the Menu of the Mainpage on my Site. I dont want this. I found out i can create a new Menu and add the Page there, but then its still displayed under some Menu on My Mainsite. I dont want this Page to be linked in any Menu. Beside that i dont want that it have any design, just a Blank Page.

And also i dont know how i creat a custom .html with the Page Editor. The only way to do so which i know is to creat a .html with a normal Editor and Upload to my Site. But this ends up in http://www.oldscool.at.ua/contact.html and the Email Code Form i wana use in it dont work.

If so, go to:

Control Painel > Page Editor > Pages management > Add new page

After you create your new page, the link to this page will appear in the site menu.
To remove the link from the site menu, but don't remove the page, go to:

Control Painel > Design > Site menu builder

Click on the X to remove the link from the site menu and click Save.

This will remove the link from the site menu, but won't remove the page.

If this was not what you wanted, I didn't understand what you trying to do.
Sorry.