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.
Dan Roku Stick (3600), Ultra (4640), Ultra (4670), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.