Visual Studio > Project > References > Manage NuGet Packages > Online > Search 'Microsoft.SharePointOnline.CSOM' > Accept and Install
Visual Studio > Project > References > Manage NuGet Packages > Online > Search 'OfficeDevPnP.Core'> Accept and Install
using Microsoft.SharePoint.Client;
using PnP = OfficeDevPnP.Core;
PnP.AuthenticationManager authManager = new PnP.AuthenticationManager();
ClientContext context = authManager.GetWebLoginClientContext("siteUrl");