Click the menus Tools -> NuGet Package Manager -> Package Manager Console to show the console in your IDE. Official documentation here.

Here you can issue, amongst others, install-package commands which installs the entered package into the currently selected “Default project”:

Install-Package Elmah

You can also provide the project to install the package to, overriding the selected project in the “Default project” dropdown:

Install-Package Elmah -ProjectName MyFirstWebsite