To begin, make sure your Roku TV and device are connected to the same wifi network. This is crucial for screen mirroring to work. Then, go to your device's settings and look for the screen mirroring option - it might be called miracast or wireless display depending on your device.
On your Roku TV, go to settings and select system, then screen mirroring. From here, you can set your Roku TV to prompt or always allow screen mirroring. If you're not sure which option to choose, don't worry - you can always change it later!