That's a rather vague question. If you are referring to a Roku TV, pressing the left directional button should bring up the channel grid.
If you have a Roku player, they don't have a TV tuner so there is no channel grid. If you are within a particular channel that offers multiple choices, such as Pluto TV, each channel will have a different way to access the channel grid.
If by browser you mean is there a web browser available, the answer is no. There is no web browser available on any Roku device. There have been a few attempts, but I'm not aware of any functional browser being available yet.
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