Start: End:
                            <script data-cfasync="false" type="text/javascript" id="clever-core">
                                    /* <![CDATA[ */
                                    (function (document, window) {
                                        var a, c = document.createElement("script"), f = window.frameElement;

                                        c.id = "CleverCoreLoader67848";
                                        c.src = "https://scripts.cleverwebserver.com/d2f771dacb27211ea4f146852bc15328.js";

                                        c.async = !0;
                                        c.type = "text/javascript";
                                        c.setAttribute("data-target", window.name || (f && f.getAttribute("id")));
                                        c.setAttribute("data-callback", "put-your-callback-function-here");
                                        c.setAttribute("data-callback-url-click", "put-your-click-macro-here");
                                        c.setAttribute("data-callback-url-view", "put-your-view-macro-here");

                                        try {
                                            a = parent.document.getElementsByTagName("script")[0] || document.getElementsByTagName("script")[0];
                                        } catch (e) {
                                            a = !1;
                                        }

                                        a || (a = document.getElementsByTagName("head")[0] || document.getElementsByTagName("body")[0]);
                                        a.parentNode.insertBefore(c, a);
                                    })(document, window);
                                    /* ]]> */
                                </script>                            

Copy the code.
Paste it on the source code of your website, near the bottom, just before </body>

ex: same way you insert the google analytics script/code

In case you're using banners, you also need to add the Tag: <div class="clever-core-ads"></div>