looks like you didnt take it out of the uhh "unzipping folder" because it says fnf-osu-mania-skin-master -> fnf-osu-mania-skin-master (which happens when you unzip stuff using the default windows zip opener). Take the second one out of the first one and into the main osu skin folder, then restart osu (or just open it if you had it closed) and then just select that skin in the "skins" section of the osu settings.