It is strongly recommended to use osu![osu.ppy.sh] for beatmap management, since it is a lot more convenient. As this is a practice client, the expected use case is having both clients installed and switching between them very regularly.

McOsu only supports osu!(stable)[osu.ppy.sh] databases, but not osu!(lazer) databases atm!

1. Create a new folder somewhere (any name works): C:/OsuStuff/
   
2. Inside this folder, create a "Songs" folder: C:/OsuStuff/Songs/
   
3. Next to the Songs folder, create a "Skins" folder: C:/OsuStuff/Skins/

After you've created this structure, configure McOsu to use the parent folder as the osu!folder in the Options menu:
Linux and macOS users don't need drive letters of course, so the example osu!folder would simply look like this: /OsuStuff/
If you're on macOS and unsure, just copy this exact folder structure: https://imgur.com/a/SgqSKgP
If you're on Linux and unsure, just copy this exact folder structure: https://imgur.com/a/srDCyOZ

Every beatmap should have its own subfolder inside the "Songs" folder from before:

1. Download a beatmap from https://osu.ppy.sh/
   
2. Create a new subfolder inside your "Songs" folder, preferably with the beatmap filename as the name: C:/OsuStuff/Songs/302303 Sheppard - Geronimo/
   
3. Rename the file extension of the downloaded osz file from osz to zip
   
4. Extract the contents of the zip file into the just created beatmap folder
   
5. If McOsu is running, you can press F5 while you are in the songbrowser to refresh/reload all beatmaps

Don't forget that only osu!standard beatmaps are supported!
Beatmaps for other gamemodes (taiko, mania, catch the beat) will simply not show up.

Every skin should have its own subfolder inside the "Skins" folder from before:

1. Create a new subfolder inside your "Skins" folder (this name will be visible in the in-game skin selection): C:/OsuStuff/Skins/MySkinNameInGame/
   
2. Copy all skin images, sounds and the skin.ini file into the just created "MySkinNameInGame" folder
   
3. You should now be able to see and select your skin in the Options menu

The two default skins which are shipped with the game, one for Virtual Reality and one for Desktop play, can be found here: /<Steam>/steamapps/common/McOsu/materials/