Upon registration you get a free trial. Notice that after the trial period the service becomes payed.

In the Elements Panel, under the Plugins dropdown, you can find the Olark Chat icon. 

Drag it to the canvas. 

Note that the chat window will be pinned in the published site, and in the studio what you see is a mockup. Meaning, you can place it on the canvas anywhere, it will not appear there when publishing.

If you wish, you may hide the mockup from the canvas by marking this checkbox. To locate it once more, use the Layers Window. If you choose to hide, do it after you finish setting up.

If you already have an account, you may now ender your site ID. Open the Manage window from the Properties Panel.

Go to installation, and copy your site’s ID at the bottom of the page.

Back in the Studio, paste the ID in the field located in the properties panel.

In the Properties Panel, Click the Manage Icon

An Olark window will pop up, there you can create an account with Olark or login if you already have one.

After registering, you can customize the appearance, behaviours & text of your chat window.

In the Studio, click publish, and see that the chat is working.

In order to chat with the visitors, go back to the Olark window and click "Launch Chat".

You can always go back to the Olark manage window and edit the chat some more, or change the location.