To install the latest PnP core, go to your Project References > Manage nuget packages.
Download the SharePointPnPCoreOnline component. Its version should be 2.20.1711 or higher (i.e Nov 2017 or higher).You also need to add the statement using OfficeDevPnP.Core.Sites; in your class.
To create a Modern team site, you can use the below code:
TeamSiteCollectionCreationInformation modernTeamSite = new TeamSiteCollectionCreationInformation { Description = "Demo Site description", DisplayName = "Demo Modern Team Site", Alias = "modernTeamSite", IsPublic = true }; var createModernTeamSite = await context.CreateSiteAsync(modernTeamSite);