How to make a javascript window pop up on click?

The question is not precise – sorry.

It is necessary that when you click on a link in the menu in the same window, for example, information about the site drops out.

Tiped to use an anchor( # ).
The menu is built in php and added to the html page.

Answer 1, authority 100%

If it’s very rude, then:

function showTab(n)
    var p = document.getElementsByTagName('p');
    for(var i = 0, pl = p.length; i < pl; ++i)
        if(i == n)
            p[i].style.display = 'block';
        else if(/(\b|\s)?tab(\b|\s)?/.test(p[i].className))
            p[i].style.display = 'none';
    return false;
<a href="#" onClick="return showTab(0);"> 1</a>
<a href="#" onClick="return showTab(1);"> 2</a>
<p class="tab" style="display:none">1</p>
<p class="tab" style="display:none">2</p>

Answer 2, authority 33%

Look aside jQuery: the main page has an example of what you need.