Uploading text content from notepad is a simple copy and paste. Click "Manage my site", then choose the page you want to edit from the "site tree" and click on it. Click "view" for the content item you want to edit from the list and then click "edit".

You can now copy and paste your text from notepad into the "Rich Text box" and depending on the page type you can also upload images /files and set other parameters. Once the content is entered click "save" and then you can click "preview" to see what the page will look like on the site. If you are happy click "publish" to send the content live.