Assuming you're referring to this plugin, your code should be:
// To Store
$(function() {
$.session.set("myVar", "value");
});
// To Read
$(function() {
alert($.session.get("myVar"));
});
Before using a plugin, remember to read its documentation in order to learn how to use it. In this case, an usage example can be found in the README.markdown file, which is displayed on the project page.