Any advice for installing Identity in existing MVC project?

My app is a single layer project targeting .NET 4.5 and MVC 5.2.3. I would like to install Identity on an existing MVC project. I plan to just...

install these packages:
Microsoft.AspNet.Identity.Core v2.2.1
Microsoft.AspNet.Identity.EntityFramework v2.2.1
Microsoft.AspNet.Identity.Owin v2.2.1

Then create a new MVC project from template with Identity and copy these classes from that into my app:
Startup.cs
App_Start>Startup.Auth.cs
App_Start>IdentityConfig.cs
Models>AccountViewModels.cs
Models>IdentityModels.cs
Models>ManageViewModels.cs

Then copy the Controller and Views from the Controllers/Views folders.

One thing I noticed is that my app doesn't even have a Startup.cs file. Its sort of a tangent, but how does this work and why doesn't my project have it, but the one I just created from template with Identity does. When does it run, and do I need to do anything special in my project to insure that it does?