In C# precompiled functions, adding NuGet libraries is the exact same process as in any traditional .NET application. In C# script-based functions (available when deployed online in the Functions Portal) the process is significantly different.
Since C# script-based functions are currently not very popular, we will not elaborate on the process here. Please refer to the Appendix A, C# Script-Based Functions for a detailed walk-through on how to add NuGet dependencies in C# script-based functions.