To start up AliRoot after installation just type
this starts AliRoot in interactive mode. When the root  prompt appears, you can start an AliRoot interactive session by creating the standard menu
root .x menu.C
The macro menu.C invokes the AliRun::Init() method. In turn this calls the configuration file Config.C where the configuration of the detector and several simulation parameters can be specified.
When the initialisation is finished the root prompt apears again and the Root control bar appears.
You can now select several actions from the menu.
generates an event with the number of tracks and the configuration as specified in Config.C. The hits deposited
generates the standard lego plots for radiation and absorption length. By default the granularity is 60 rays in theta and 60 rays in phi.
To view the results when this command is finished type:
root .x lego.C
the parameters of the lego run can be specified in the calling sequence of the RunLego method as follows:
root gAlice->RunLego (your list of parameters)
see AliRun::RunLego for details
This shows a new menu from which you can draw the geometry tree for the Alice detectors. Clicking with the right button on the pad with the name of a geometrical element gives access to a number of graphic and inspect functions. Double-clicking on the pad generates a drawing of the specifications of the geometry of the element.
From this menu you can draw pretty pictures of the major ALICE components. Note that some pictures may take a long time to be produced.
To quit AliRoot
root [ ] .q
After startup of the aliroot program the simulation infrastructure is initialised by the AliRun::Init() method. This method takes an argument that is the name of the initialisation script. The default name for this script is Config.C. This script initialises the version of the different detectors and of the generator to be used. In particular some generators can generate a fixed number of particles and in this case this number is an argument of the generator constructor.
A global variable gAlice holds the pointer to the instance of the AliRun class.
root [ ] gAlice->Init()
The Init method loads the chosen MonteCarlo (for the moment only Geant3 is available in production) and initialises it. Another global variable gMC holds the pointer to the instance of the virtual MonteCarlo Class AliMC. This allows to access all the functions of the Virtual Monte Carlo interface. Some of the functions are specific to Geant3, and these can be accessed recasting this pointer to a specific Geant3 pointer via the statement
root [ ] TGeant3 *g3 = (TGeant3*) gMC
In particular all the drawing functions of Geant3 are available via this interface. To draw a cut view of the ITS the following commands can be used
root  TGeant3 *g3 = (TGeant3*)gMC
root  g3->Gsatt("*","seen",1)
root  g3->Gdrawc("ITSV",1,.1,10,10,.125,.125)
Note that several TGeant3 functions are also available by clicking with the right button on a canvas while in the AliRoot session.
The AliRun::Run() method starts a run composed by a single event. This method takes as argument the number of events to be processed. If this number is negative, the run is not terminated and more events can be run. If this number is positive, after the indicated number of events the run is terminated. No more events can be run.
In AliRoot there is really no difference between batch and interactive processing. An elementary macro to run AliRoot in batch mode is provided amongst the examples, and it can be used in the following way to run a 10 events run
aliroot -b grun.C\(10\)
Note that the backslashes are necessary to prevent the shell from interpreting the brackets.