Click 'Install', then next, continue, finish, etc.Once signed in, go to your Steam Library tab and go to Age of Empires II in the left sidebar.After Steam has finished updating (it updates often!) you can sign in.After the install is completed, click the play icon next to 'Age of Empires 2 HD' in the left sidebar.Click continue, yes, next, install, etc.If asked to choose an application, select 'Porting Kit' and 'Always use this application'.Copy and paste this into your browser address bar, then press enter: pkid://385.