Extract the plugins folder from the zip into Valheim\BepInEx\plugins\Truncated-DiscoverySync\ on all clients and the server.
Both DiscoverySync.dll and DiscoverySync.Core.dll are needed on all installs. BepInExPack_Valheim and Jotunn must also be installed.
Updating from a version before 1.0.2: delete the old Translations folder in Valheim\BepInEx\plugins\Truncated-DiscoverySync\ before extracting the new files. Older versions kept each language in its own subfolder (such as Translations\English\DiscoverySync.json). Jotunn still loads any subfolders left behind, so every language would load again. From 1.0.2 the Translations folder holds one file per language, named like DiscoverySync-en.json, with no subfolders.