Question from newbie installing Yii2 advanced

Howdy! I’d idea to install Yii2 framework. It’s almost done, but I had no idea how to work with Apache. They said: +++Set document roots of your web server: for frontend /path/to/yii-application/frontend/web/ and using the URL http://frontend/ for backend /path/to/yii-application/backend/web/ and using the URL http://backend/ ++++

I did this in console:

sudo nano /etc/apache2/sites-available/default 

Than I wrote this:

<VirtualHost 127.0.0.1:80>
    ServerName myserver.com
    ServerAlias 127.0.0.1
    DocumentRoot /var/www/html/yii/frontend/web/

<VirtualHost 127.0.0.1:80>
    ServerName admin.myserver.com
    ServerAlias 127.0.0.1
    DocumentRoot /var/www/html/yii/backend/web/
</VirtualHost>

And there is nothing. What I have to do?

Big thanks for everybody!