If you're referring to User-Made Levels:
When launching the game and clicking past the title screen, you are shown the list of all currently ranked levels in order of ascending difficulty. If you would like to view unranked maps, click the podium icon next to the search bar above the list of ranked levels (That's also where the rest of the search filters are located)
If you're referring to Songs uploaded to the game by users:
You can get to this screen by clicking the menu icon in the top left corner and clicking on the "Songs" option. Note that "Songs" in this context are NOT the same as "Levels," and you won't be able to play or find any levels on the songs page, click the menu icon and go back to the Levels page to find online levels. The songs page is where you can upload and find music to use in your levels, and each song displays their corresponding Song ID that you can put into the editor to use that song in your own level.
Hope this helps, otherwise if you need more clarification on anything feel free to reply to this post or message me over on the Pulsus Discord Server
Thanks for playing! o/