void MacroName ( ) {
< . . .
your lines of CINT code
. . . >
}

The macro is executed by typing
> root MacroName . cxx
at the system prompt, 

or it can be loaded into a ROOT session and then be executed by typing
root [ 0 ] . L MacroName . cxx
root [ 1 ] MacroName ( ) ;
at the ROOT prompt. 

Note that more than one macro can be loaded this way, as each macro has a unique name
in the ROOT name space. Because many other macros may have been executed in the same shell before, it is a
good idea to reset all ROOT parameters at the beginning of a macro and dene your preferred graphics options,
e. g. with the code fragment

// re-initialise ROOT
gROOT->Reset ( ) ; // re-initialize ROOT
gROOT->SetStyle ( "Plain" ) ; // set empty TStyle (nicer on paper)
gStyle->SetOptStat (111111) ; // print statistics on plots , ( 0 ) for no output
gStyle->SetOptFit (1111) ; // print fit results on plot , ( 0 ) for no ouput
gStyle->SetPalette ( 1 ) ; // set nicer colors than default
gStyle->SetOptTitle ( 0 ) ; // suppress title box
. . .

Next, you should create a canvas for graphical output, with size, subdivisions and format suitable to your needs,
see documentation of class TCanvas:
// create a canvas , specify position and size in pixels
TCanvas c1 ("c1","<Title >",0,0,400,300);
c1.Divide(2,2); // set subdivisions, called pads
c1.cd(1); // change to pad 1 o f canvas c1