First download and install .NET 5 (.NET Runtime or SDK) for the platform you are using.
Once you have .NET 5 installed, clone the OpenCoreMMO repository to your machine
bashgit clone https://github.com/caioavidal/OpenCoreMMO.git
bashcd srcdotnet run -p "NeoServer.Server.Standalone"
OCM Server starts with a 1/1 account with some players loaded.