Tradition and Scripture are both rooted in history. First there is the coming of Christ into history, his life, teaching of the apostles, death, resurrection and ascension. He gave them the command to teach, baptize and directed them to repeat what he had done and said at the Lord Supper as a memorial. Christ did not write down anything, nor did he tell the apostles to write but to do what he commanded. This is the beginning of Church tradition. The apostles and Paul traveled far and wide converting Jews and Pagans and establishing groups of believers or Churches in the Greek and Roman world. They taught, preached, baptized and celebrated the Lord's Supper, etc.
At first the Jewish Christians went to the temple or synagogue service to hear the Old Testament Scriptures, the actual celebration of the Lord's Supper took place in individual homes. Gradually the Mass developed its own liturgical form and church buildings were erected to accommodate the increasing number of Christians.
Those who insist on scripture alone as the source of faith have no ground to stand on because there was no New Testament but only Tradition, the passing on of the faith by teaching, preaching and liturgical functions.
These are the approximate dates when the gospels were written:
Mark (55-70 AD)
Luke (before 62 AD)
John (80-90 AD)
Acts (62-70 AD)
The apostles, especially St. Paul wrote letters to the Churches. In one of these St. Paul affirms traditions taught by him. Most of these letters were written between 50-85 AD and nothing that we know of were written prior to 50 AD. This means that for about 20 years and beyond after the death of Christ tradition only was the de facto way the Church operated. And it took time for scripture to come into being and to be universally accepted as inspired.
Besides baptism, we find other sacraments mentioned in Scripture such as forgiveness of sins and anointing of the sick but no description was given of them because it was presumed that Christians knew how they were practiced. The Letters of the Apostles were the beginning of Scripture and some have become part of the New Testament.