How to set startup object / project in visual studio?

To debug any project in visual studio,  you must set a startup object as the below error 

you can set a startup object easily, just right click on your object and click set as a startup object 

also, you can set the project as a startup project for your solution 

right click on your project  and click set as a startup project  

Or, right click on your solution and click set startup projects 

and select one of your projects 

also, you can set multiple projects as a startup 

Thanks.