You can find steps for downloading Datomic at Get Datomic. For getting started, Datomic Starter or Datomic Pro is required. Datomic Starter is free to download and use, but does require that you register by creating an account at My Datomic first. Datomic requires the Java 8 JDK.
Once you've downloaded Datomic, unzip it somewhere locally. Throughout the documentation, shell commands are run from the root directory of the Datomic install. Change to this directory now, e.g.:
Next: Connecting to a Database