Almost all the code we use from external sources is free and open source. Anybody can download and use it. However, creating a good site, even when using sophisticated CMS (content management systems) such as Joomla, WordPress, Moodle etc can be quite time consuming. You will also need to find somewhere to host it. You will need to ensure that your chosen hosting company provides you all the resources that you need, e.g. Apache webserver, MySQL database and PHP programming language.
Moreover, anything you put on the web will inevitably become the target of hackers and crackers. So, in addition to creating your site, you will also need to maintain it - not merely with fresh content but with frequent security updates. Some internet hosting companies will do the security patches for you. Other's don't. Some companies (such as Bytemark - our provider) allow you to have root secure shell (SSH) access to your server so you can do the patches yourself. In fact, this gives you near total control over your server. However, with great power comes great responsibility, which means you have to do all the software maintenance yourself! So, if you follow the DIY route, please make sure you read the small print before you commit yourself!
When we create sites for our customers and host them here on the DEOSS Community Webserver, we take care of all the security updates and server upgrades for you, so you don't have to worry about them. We also take complete and incremental backups of your site to a remote server using a Unix application called RSync. So all you have to do is upload your content and leave the tricky, techy stuff to us.