Join Michael Duquet for an in-depth discussion in this video How does Optimizely work?, part of Optimizely Fundamentals.
When to use Optimizely will differ for your organization. In general, you have your control or baseline experience, the status quo. Unfortunately, you've encountered a problem with the status quo. This could be low conversion rates. This could be a high exit rate or a bounce rate on a page and you just don't understand why. There could be one of several different solutions. What you do as a conversion rate optimization tester is form hypotheses and when you get approval from your organization to say, you know what? I should test that. That's where Optimizely comes in. We just covered a lot of information here, but hopefully you now understand that Optimizely can help manipulate what's actually displayed on the website.
To better understand the technical instructions of Optimizely, you can consult the Optimizely FAQ section in their community to get a full rundown. For most organizations and individuals, however, the most important thing to understand is that you need to have a need to find out why conversions or actions are not being taken. That desire to change and improve is what Optimizely is all about.