Yes, by default an experiment is activated on all of your web pages. You can also choose to customize on which pages an experiment should be activated. For example you can define to activate an experiment only if the path of an URL starts with “/blog” and has a URL parameter “language”. There is also a tool in the Experiments creation wizard which lets you test whether users would enter an experiment on a given URL or not.

Previous FAQ: Is it possible to change the confidence threshold / statistical significance needed to decide a winning variation?