To use the Experimenter you need to have two or more blocks. You can add the blocks as you normally would. Then, add the Experimenter block. You will be able to choose to randomize the block that is displayed "Per Visitor" or "Per Pageload". "Per Visitor" is usually the choice you want (so that individual users have a consistent experience as they visit and nagivate your site). For every block that you want to be part of the experiment you need to click on it and then choose "Design", go to the "CSS" tab and add the "experiment#" class. There are specific instructions for this on the block once you add it to your page.

In order to "count clicks" for analytics, every block in your experiment should have at least one link in it. This can be text, an image, or anything else that is a link. You can use any type of block. Usually you will want to use the Content block.