The Darkweb is the "secret" internet that's under the radar of Google and only accessible with special software such as Freenet and Tor.
The Darkweb is usually used by those that want to preserve their anonymity online or those suffering political repression on the normal internet (referred to on the Darkweb as "Clearnet"). However, because it grants maximum anonymity, it's also a haven for criminal activity so be warned there is a quite a lot of illegal content on Darkweb.
Freenet is a Java based application that connects you to other Freenet users. Traffic and content is bounced and shared around different users meaning its almost impossible to trace who is using it and what they are looking at. Freenet installs a client in your Menu Bar from where you can activate and deactivate Freenet at anytime. Note that Freenet only allows you access to Freenet - you can't surf the normal net with it anonymously unlike with Tor.
When you setup Freenet, you're offered a range of security settings from Low to Maximum depending on how secure you need it to be. The Maximum setting offers the slowest surfing speed but its also the most secure and prevents any trace of content being left in your cache.
Freenet is very basic in look and functionality. Freenet pages are simply hyperlinks which “download” to your computer and can take quite a while to open. The first page you're presented with is a handful of links of which the first one "Linkageddon" is the main gateway to the majority of content on Freenet. There is a clear warning next to this link that some of the material is highly offensive and Freenet is certainly not suitable for minors.
Freenet is an interesting freedom of information project that harks back to the old days of the internet although users should be warned that much of the content is highly offensive or illegal.