From the Website Management section, go to Architecture, under the Structure column
Scroll down and click “Add widget”
Click “Text/HTML”, then click “Select & Configure”
Change the “Internal Title” to “Olark”, then click “Create Widget” in the lower left-hand corner
Hover your mouse over the new widget and click “Enable”
Back on your website, click on the new button in the sidebar labeled “Edit section HTML”
Change "WYSIWYG" to "RAW HTML", then paste in the code from below or http://www.olark.com/install
Click “Save & Close” in the bottom right-hand corner. That’s it!