Note: These steps are taken from a reply posted by Rocky

In order to run/debug the Blazor sample.
You need to launch not just the Blazor client, but also the app server project, 
just like you would with the WinForms or WPF apps.

Right-click on the solution, select 'Set Startup Projects'
When dialog appears select the radio button  'Multiple startup Projects'

Set Action for the project 'ProjectTracker.AppServerCore' to 'Start
Also set Action for the project 'ProjectTracker.Ui.Blazor.Client' to 'Start'

Create a file explaining to run Blazor
Create a file explaining to run Blazor

Its actually a reply by Rocky to a question posted on Csla forum