Startup.cs file is called by the main program which is existed into the program.cs.startup.cs which is the mandatory file in asp.net core application without that file asp.net application cannot be executed and first asp.net framework see the configuration of this particular file.By using the startup.cs file we can make some configuration which are responsible to respond http request
By using the configure method we can configure the asp.net request pipeline by using some middleware components. Whenever our application is started asp.net framework first watch configure method and execute method statements. By passing dependencies in configure method to make some configuration but at this time I am not going to discussing about them. All the middleware components are configured by using the extension method of IApplicationbuilder class. IApplicationbuilder class may be used to set routes(Routing) for application.
The ConfigureServices method
By using the configuration services we can pass connection string of database server we can add MVC libraries using this method we can set SMTP services by using this method and many more.