How to use Nuget assembly as files with visual studio community

I am starting a new coding job with a new client.
The problem I am having is that a lot of issues with namespaces that can not be found or maybe missing directives or an assembly reference. This, I think, is a common thing. So I am wondering where I can download a free DLL from Microsoft that will do the trick and get me to compile my code. The class the code is using that the compiler does not like is "GeoPoint".
A quick search online offered using nuget to install the package Azure.Core.
So, how do I do this? I am using Microsoft Visual Studio Community 2019. I am looking for some direction. Please advise.

On my work computer, I went to https://azure.microsoft.com/en-us/downloads/ in my browser but it is blocked. So, I am assuming now that I have to use visual studio itself to add new assemblies instead of using a browser. Is that right or do I have to ask my administrator for access?

The page:
https://www.nuget.org/packages/Azure.Core/
offers me another hint with "Package Manager"
I found under Project->Manage Nuget Packages..." in visual studio but when i try to uplad a package I get an error message.

So, my manager said I fist need to download an assemply.

Please advise.