tool tip problem

  var skin1 : GUISkin;
  var a1 : boolean ;
  var a2 : boolean ;
  var a3 : boolean ;
  var a4 : boolean ;
  var a5 : boolean ;
  var a6 : boolean ;

  function Start()
  {
  a1 = true;
  a2 = true;
  a3 = true;
  a4 = false;
  a5 = false;
  a6 = false;
  }

  function OnGUI ()
  {
  GUI.skin = skin1;
  GUI.Box(Rect(3,800,808,35), " ");
  if(a1 == true)
  {
  GUI.Button(Rect(3,810,80,35),GUIContent (" START", "click to start "));
  a4 = true;
  }
  if(a2 == true)
  {
  GUI.Button(Rect(85,810,80,35),GUIContent (" CONTINUE", "click to continue"));
  a5 = true;
  }
  if(a3 == true)
  {
  GUI.Button(Rect(167,810,80,35),GUIContent (" EXIT", "click to exit"));
  a6 = true;
  }
  if(a4 == true)
  {
  GUI.Label (Rect (10,100,300,40), GUI.tooltip);
  }
  if(a5 == true)
  {
  GUI.Label (Rect (10,400,300,40), GUI.tooltip);
  }
  if(a6 == true)
  {
  GUI.Label (Rect (10,600,300,40), GUI.tooltip);
  }
  }

here my need is i have box over which three buttons are there start,continue and exit when mouse is over the button start i should display click to start when mouse is over the button continue i should display click to continue for that i used tool tip but when mouse is over start button it is displaying correctly but when mouse is over continue button the position of tool tip label remain in the same area as start button

First of all your variables a4 - a6 doesn't make any sense since they get set to true every frame. Furthermore it would be better to give your variables descriptive names like i did.

If you really need different tooltip positions you could do something like that:

var startButtonVisible : boolean = true;
var continueButtonVisible : boolean = true;
var exitButtonVisible : boolean = true;

function OnGUI ()
{
    GUI.Box(Rect(3,800,808,35), " ");
    if(startButtonVisible)
    {
        GUI.Button(Rect(3,810,80,35), GUIContent (" START", "start"));
    }
    if(continueButtonVisible)
    {
        GUI.Button(Rect(85,810,80,35), GUIContent (" CONTINUE", "continue"));
    }
    if(exitButtonVisible)
    {
        GUI.Button(Rect(167,810,80,35), GUIContent (" EXIT", "exit"));
    }  
    switch (GUI.tooltip)
    {
        case "start"    : GUI.Label (Rect (10,100,300,40), "click to start"); break;
        case "continue" : GUI.Label (Rect (10,400,300,40), "click to continue"); break;
        case "exit"     : GUI.Label (Rect (10,600,300,40), "click to exit"); break;
    }
}

ps. You really should use any kind of code-indentation otherwise it's really hard to read the code and it's much harder to spot a missing bracket.

You may also take a look at GUILayout. It’s much easier since you don’t need to struggle with rect positions. You still be able to controll the layouting eg. with GUILayout.Width you can define a fix width for an element.

Finally if you haven’t read it, take a look at the FAQs and the Editing Help.