The previous link showed how to get started with using Athena. You should now have a work directory set up for the release you wish to use. If your requirements file contains 'apply_tag setup' (as shown here) then athena should already be setup. If not, you can either explicitly source a setup script in the AtlasOfflineRunTime package (as shown here, for example) or check out a package that will setup a runtime environment for you, such as UserAnalysis or TestProject (release 12 or later).
The following jobOptions files should be available for you to use as part of the main release:
To get one of these scripts, simply do get_files SCRIPTNAME. More explanation about the jobOptions scheme used for Atlfast is available here. Those files beginning with 'POOLtoAtlfast' read in generator-level information from a previously-created POOL file. The default used is a file I chose at random but you can change this to your favourite by altering the line
Those beginning with 'PythiatoAtlfast' run the Pythia generator to produce gg->ttbar events, again a random choice. All four scripts then run Atlfast before creating output that you can use. Those ending in 'AtlfasttoAAN' create an Athena Aware Ntuple. The ntuple file is named 'CBNTAA.pool.root' by default but this can be changed by altering the following line
Once you have decided which script you would like to run and modified it accordingly, run it like this
This runs over just 50 events, but you can modify the number to something more suitable.