Does Roku require internet?

Could you please clarify if Roku, a popular streaming device, necessitates an internet connection for its full functionality? Are there any basic functions that Roku can perform without being connected to the internet? Is it a prerequisite for streaming content, updating firmware, or accessing certain features? And if internet is necessary, are there any specific speed requirements or limitations that users should be aware of? Understanding these aspects would greatly help potential users make an informed decision regarding Roku's usage.