First, you need to create all the logins on NM that are used in the db you copied there. You can script out the logins from the old server, but you'll need to correct the password and remove any "DISABLE" login statements. [You can add the login's current SID on the CREATE LOGIN statement if you'll need to keep going from one server to another, as that will making sync'ing automatic.]

Then, if you didn't copy the existing SIDs, you'll need to run the ALTER USER command for every user to re-sync it to its login.