Again, you aren't giving details. Did you have an interview? Are you from a visa-exempt country?
Decision made means just that, they have made a decision on your application. Usually this is good news. They don't just mail you a visa, they will either request your passport then mail it back with the visa and with your COPR, or if you are visa-exempt, they will just mail you the COPR. The time this takes varies with every visa office.