Below I have supplied the "basic" information required to achieve "understanding" of how the data is stored a accessed; this information has come directly from the Freenet web site. I would suggest viewing the following, "Understand Freenet" ,if you wish to read further.
How can many people access a freesite if they aren't the author (and can't decrypt it)?
All Freenet nodes contribute with a part of their harddrive space to
store files. The files are stored encrypted in the store-directory in
the Freenet installation directory.
Unlike other peer-to-peer networks, you as a user has little or no
control over what is stored in your datastore. Instead, files are kept
or deleted depending on how popular they are. This is to ensure that
Freenet is censorship resistant. The only possible way to remove
something from Freenet is to not search for it, and hope that
everybody else does the same.
It is hard, but not impossible, to determine which files that are
stored in your local Freenet Datastore. This is to enable plausible
deniability as to what kind of material that lies on your harddrive in
The initial diskspace allocated for the datastore is 5% of available
disk space if it is over 20GB, 10% if it is over 10GB, 512MB if under
10GB, and 256MB if under 5GB. You can change the store size at any
time, the more the better, both for your personal browsing and for
Freenet as a whole.
Initially, each node has no information about the performance of the
other nodes it knows about. This means that routing of requests is
essentially random. But since different nodes have different
randomness, they will disagree about where to send a request, given a
key. So the data in a newly-started Freenet will be distributed
As more documents are inserted by the same node, they will begin to
cluster with data items whose keys (see below) are similar, because
the same routing rules are used for all of them. More importantly, as
data items and requests from different nodes "cross paths", they will
begin to share clustering information as well.
The result is that the network will self-organize into a distributed,
clustered structure where nodes tend to hold data items that are close
together in key space. There will probably be multiple such clusters
throughout the network, any given document being replicated numerous
times, depending on how much it is used.
Each file that exists on Freenet has a key associated with it. Freenet
0.7 has various types of keys. Keys are used for everything on freenet, and are a kind of URI (e.g. freenet:=KSK@sample.txt).
Most keys are hashes: there is no notion of semantic closeness when
speaking of key closeness. Therefore there will be no correlation
between key closeness and similar popularity of data as there might be
if keys did exhibit some semantic meaning, thus avoiding bottlenecks
caused by popular subjects.
If you are interested, here is a direct link to Ian Clarke's paper "Freenet: A Distributed Anonymous Information Storage and Retrieval System" hosted by the computer science department at the University of Iowa.