Answer to your question would actually end up being a full tutorial.
That said, I suggest that you visit the following website and get yourself familiar with Entity Framework Code First concepts:
http://www.entityframeworktutorial.net/code-first/entity-framework-code-first.aspx
Mentioned tutorial has both conceptual overview as well as code samples.
Once you are done with tutorial, you will understand the following code snippet:
public class ApplicationContext : DbContext
{
public DbSet<Company> Companies { get; set; }
}
Then you need to create adequate migration and apply it to your database which will end up with creation of "Companies" or "Company" table (depending on EF version you are using).