I tried to follow the tutorial video No. 9 and it created the symbolic links in my 'multisites/slave1' directory.

But even if the structure and templates were copied, I only see a default joomla installation without content or my chosen template.

In my master, the new slave has the new DB settings, but when I log into the slave administration, the configuration is identical to the master.

How do I separate the slave from the master? I want the slave to use the same components, but with a different database and a different Joomla template.

If when you login in the slave site, you see the content of the master, this probably mean that in fact you are logged into the master and not in the slave site.

Verify the "Global Configuration" to check the DB connection and see if you are on the master DB or on the slave site DB (or prefix).

I suppose that you probably didn't spelled the slave site domain name correctly.
It is case sensitivie and perhaps you have forgotten to put the domain with and without the WWW

When a domain name does not match exactly the URL then this is the master website that is displayed.

I have solved the problem. Not all tables were copied from the master to the slave1. After manually copying the missing tables, all was fine. But I wanted empty tables, so I just left the slave1 where it was.

After that, I just used "New like" and used the slave1 as template to create the rest of the slaves and the normal Joomla installation process appeared for each site. After doing the setup process for all sites all is fine.

New question:

After creating the slaves, how can I distribute new Joomla Webpage Themes in the master Joomla directory to the slaves?

The already present ones were all linked fine to the slave directories, but if I add new Joomla Theme to the master templates directory, they do not get automatically linked to the slave template directories.

How do I do this?

Concerning the Joomla Templates, all depends the version of Joomla.

In Joomla 1.5, the new template installed are automatically discovered by Joomla.
In Joomla 1.7, joomla has changed their process and you have to go in the extension manager and "discover" sub menu. There you can discover the template and ask to install it in the slave site. This is a new behavior created by Joomla.