# Getting Started The usage section of the docs explores the intended use of Refract, focusing on each concept or feature in isolation. If you are unfamiliar with reactive programming, we recommend reading Andre Staltz's article [The introduction to Reactive Programming you've been missing](https://gist.github.com/staltz/868e7e9bc2a7b8c1f754) before reading these docs. Reactive programming is central to Refract, so some understanding of the paradigm will be essential. Before we begin, below is a quick explanation of some new terms associated with Refract which we will use throughout the documentation. Each will be more thoroughly explored through examples, but starting with a rough approximation in mind will help. ## Aperture An `aperture` controls the streams of data which enter Refract. It is a function which observes data sources within your app, passes this data through any necessary logic flows, and outputs a stream of `effect` values in response. ## Handler A `handler` is a function which causes side-effects in response to any `effect` value output by the `aperture`. ## Error Handler An `errorHandler` is a function which causes side-effects in response to any `error` value output by the `aperture`. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://refract.js.org/usage/getting-started.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.