The world changed when humanity unlocked the Nexus (or the Nex for short). The Nex Glossary provides several definitions of some of terms that developed thanks to this monumental discovery.
The interactions between the physical world and the Nex sometimes get a little complex. Nex Interactions provides a reference to answer most of the scenarios that come up at the table.
The Han Cluster has a rich and fascinating history. You can read about it here.