Explain How the Old Testament and the New Testament are different?

The biggest difference is in the Old Testament any christian was a christian because they new Jesus was coming and was going to die on the cross, in the New Testament they got to be with Jesus, they saw Him and most beleived. In the new testament till now we believe that Jesus died on the cross for our sins and that through Him we can go to heaven. So the main thing is people believed that Jesus died for their sins and for the Old Testament they believed He was coming.