Show jQuery popup only at first visit of a page

You can use localstorage. It is easy to understand and use.

$(document).ready(function() {
    var isshow = localStorage.getItem('isshow');
    if (isshow== null) {
        localStorage.setItem('isshow', 1);

        // Show popup here
        $('#jPopup').show();
    }
});

It will show you the popup at first visit of your site.

You may use SessionStorage or LocalStorage for this as per your need.

If you need to do only for that session, use SessionStorage. If it should be stored permanently in the user's browser, use LocalStorage.

    $(document).ready(function(){
        if(sessionStorage && !sessionStorage.getItem('isshow')){
            $('#jPopup').show();
            sessionStorage.setItem('isshow', true);
        }
    });