This differs greatly webhosting provider. This chapter just summarizes basics you need to know to edit pages on your web site or to upload new pages.
Before you can start editing/uploading, you need to connect to server of your provider. To do that you need to know at least address of the server, your account username, your account password and file protocol to use. You get these data from your provider once you sign up.
You will fill these into Login dialog of WinSCP. Note that Host name box is where you fill address of the server, be it domain name (such as ftp.example.com) or IP address. Also note that the name of the server, where you connect to manage the web site may not be the same as your web site domain.
If you do not know what protocol to use, choose FTP as it is most common case (note that WinSCP defaults to SFTP). But if you have choice, use SFTP, as it is secure one.
You can save the login data to stored session using Save button, so you do not need to type everything each time.
Once you are connected, make sure you are in the remote directory dedicated to store a web pages. It may be the one you get in after logging in (it is the case if you do not see any subdirectories after logging in). But with some providers you will have several subdirectories available, from which only one is visible on the Internet. Such subdirectory will have a name like www, htdocs, httpdocs, public_html or other.
All files you upload to this directory will be visible on the Internet. So for example if you upload your page pictures.html into your web directory htdocs and your site domain is example.com, anyone will be able to see your page at address http://example.com/pictures.html.
By convention there is a single file that gets displayed if you do not specify any file in the address directly, i.e. frontpage. The name of the file is usually index.html or index.htm (or different extension if you use some scripting language).
Before you start uploading/creating pages, make sure you use reasonable file names. It is strongly recommended not to use punctuation characters, spaces and some special characters in filenames to be published on Internet. Hence instead of Mein Gästebuch.html, use mein_gastebuch.html.
Also URL (web addresses) are case sensitive, which is different to how Windows treat filenames. So if you first test your pages locally on Windows and links stops working once you upload the pages, it is probably for inconsistencies in letter cases. For example you may have a link to Mein_Gastebuch.html, but the file is actually named mein_gastebuch.html. This is not the same on Internet.
You may start uploading by dragging your files to remote panel of WinSCP. You can drag the files either from local panel (if you are using Norton Commander interface) or from Windows Explorer.
Read documentation for other means of uploading files.
If you do not need to maintain your files locally, you can edit them directly on the remote server.
If you want to create the new page, either create new file locally and upload it. Or use File(s) > New > File command.