Run it:
root -l

Open a file:
TFile *_file0 = TFile::Open("..... .root")

File browser:
TBrowser <name>

List the directories:

.ls
<directory name>.cd()

Print the tree:
ntuple.Print()

Scan the tree:
ntuple.Scan("name of a Branch.name of a leaf")

Make a new histogram:
TH1F *name_of_the_histogram = new TH1F ("name","title",<#ofXaxis>,<#ofYaxis>,<#ofBins>);
 
Make a new canvas:
TCanvas *c1=new TCanvas ("name","title",1);

Draw a histogram:
name of the tree in the file.Draw("name of a Branch.name of a leaf")
2D histogram:
name of the tree in the file.Draw("name of a Branch1.name of a leaf1:name of a Branch2.name of a leaf2")

histogram with cut criteria:
<name of the tree in the file>.Draw("<name of a Branch1>.<name of a leaf1,name of a Branch2>.<name of a leaf2><cut criteria>")
draw two histogram in one canvas:
<name of the tree in the file>.Draw("<name of a Branch1>.<name of a leaf1>")

<name of the tree in the file>.Draw("<name of a Branch2>.<name of a leaf2>","","SAME")
e.g.:
tree.Draw("pelectron_1.tight:pelectron_1.loose","pelectron_1.tight>-1")

Open an AOD file in root:

gSystem->Load("libFWCoreFWLite");
AutoLibraryLoader ::enable();
TFile *_file0 = TFile::Open("rfio:/castor/cern.ch/user/........ .root")
TBrowser b

TChain:
Chain.C:
#include <TChain.h>

void Chain(){
  TChain tree("stopAnaMod/tree");
  tree.AddFile("stopAnaNtuple_noselection_Chowder_00.root");
  tree.Draw("event");
}

Save a histogram to .eps:
TCanvas *c1=new TCanvas ("name","title",1);

<name of the tree in the file>.Draw("<name of a Branch>.<name of a leaf>");
c1->SaveAs("name.eps");

Usage of MakeClass :

-- AnitaKapusi - 29 Jun 2009