How to add javascript function into another?

Depends on how you add it. If you add it as innerHTML and compose function calls with text, you could do that. If you add it with element creation, you could do it too but would be a little bit different way of adding function call to the page. It would be better to have function definition in an external javascript file and include the source at the top of the page, so you can call it whenever and wherever you want in the page.

function insCell()
{
var x=document.getElementById('tr2').insertCell(1);
var y=document.getElementById('tr1').insertCell(1);
y.innerHTML= 'Day 1';
x.innerHTML='<input type = "text" name = "day">onmouseover="if (timeoutId) clearTimeout(timeoutId);window.status='Show Calendar';return true;" onmouseout="if (timeoutDelay) calendarTimeout();window.status='';" onclick="g_Calendar.show(event,'frm.day',true,'yyyy-mm-dd'); return false;"><img src="images/calendar.gif" name="imgCalendar" width="34" height="21" border="0" alt="">';
}

Here the code that i having problems with. I was thinking is there a need to append for that sentence in red and how can i append?

Arranging your code:

function insCell()
{
    var x=document.getElementById('tr2').insertCell(1);
    var y=document.getElementById('tr1').insertCell(1);
    y.innerHTML= 'Day 1';
    x.innerHTML='<input type="text" name="day" onmouseover="onOver();" onmouseout="onOut();" onclick="onClick();"><img src="images/calendar.gif" name="imgCalendar" width="34" height="21" border="0" alt="">';
}
function onOver() {
    if (timeoutId) clearTimeout(timeoutId);
    window.status='Show Calendar';
    return true;
}

function onOut() {
    if (timeoutDelay) calendarTimeout();
    window.status='';
    return true;
}

function onClick() {
    g_Calendar.show(event,'frm.day',true,'yyyy-mm-dd'); 
    return false;
}

There were typos.

Thanks!it work! but my calendar is unable to work now.

Does not work either

Hey! i solved it already! Thanks a million to you!