Michal,
I have modified your code to show the two possibilities of annotation.
Some remarks:
 - TH1::Draw erases the current pad by default. Everything drawn before
   is erased.
 - When you specify the axis titles, you can give blanks at the end
   of the title strings. Blanks will be taken into account.
 - When you want to draw a text at a fixed position on a picture,
   independently of the picture range, you can set the Normalized Device
   Coordinate (NDC) option in the text object.
 - I have removed the part of your code reading your data file 
  (not available) and I am filling one bin only.
 - The function below is directly executable.
Rene Brun
void Be()
{
   Int_t NBINS = 173;
   Int_t NLINES = 34;
   char sline[80];
   Int_t  ii, jj;
   TCanvas *c1 = new TCanvas("c1","Be Isotopes", 900, 700);
// Create Be histogram
 Float_t xmin = 4.22;
 Float_t xmax = xmin + (float) NBINS * 0.05;
 Be_hist = new TH1F("Be_hist", "Be Isotopes", NBINS, xmin, xmax);
 Be_hist -> Fill(6,10);
 Be_hist -> SetXTitle("Calculated Mass      ");
 Be_hist -> SetYTitle("No. of Events per 0.05 Mass Units         ");
 Be_hist -> Draw();
 TText *xlabel = new TText();
 xlabel-> SetNDC();
 xlabel -> SetTextFont(1);
 xlabel -> SetTextColor(1);
 xlabel -> SetTextSize(0.03);
 xlabel -> SetTextAlign(22);
 xlabel -> SetTextAngle(0);
 xlabel -> DrawText(0.5, 0.04, "Calculated Mass");
 TText *ylabel = new TText();
 ylabel-> SetNDC();
 ylabel -> SetTextFont(1);
 ylabel -> SetTextColor(1);
 ylabel -> SetTextSize(0.03);
 ylabel -> SetTextAlign(22);
 ylabel -> SetTextAngle(90);
 ylabel -> DrawText(0.06, 0.5, "No. of Events per 0.05 Mass Unit");
 title = new TPaveLabel(0.1, 0.94, 0.9, 0.98, "Be Isotopes");
 title -> SetFillColor(16);
 title -> Draw();
 
}