Example Entity Framework 6 context using connection string in app.config

app.config

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <connectionStrings>
    <add name="Store" connectionString="Data Source=(LocalDb)\v11.0;Initial Catalog=Store;Integrated Security=SSPI;" providerName="System.Data.SqlClient" />
  </connectionStrings>
</configuration>

Product.cs

public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
}

StoreContext.cs

public class StoreContext : DbContext
{
    // base name=[ConnectionStringName]
    public StoreContext() : base("name=Store") { }
    public DbSet<Product> Products { get; set; }
}