Managed and unmanaged solution used in which scenario

Hi All,

My question is i have a 4 instance of my crm, test environment, dev environment, prepoduction environment and production.

see the below scenario-

1)if i have a custom code which  i am  develping in dev env then i need to test this code in test env which kind of solution is created for this managed and unmanaged.

2)if the development is correct and testing is also correct then you need to deploy to preprod and prod env which kind of solution you created at this point of time.

every time requirement is changed. you need to develop according to this,

please explain me.

Thanks & Regards,

Jyotsna